You have a keyboard that only has these 4 buttons:
<code></code>Button 1: Print an 'A' on the screen
Button 2: Select the whole screen
Button 3: Copy the selected text to buffer
Button 4: Print buffer on the screen and append it to whatever is on the screen.
You are allowed to press the keyboard N times, return the maximum number of 'A's you can print on the screen.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: N = 3
Output: 3
Explanation: 
We can print at most 3 A's on the screen by pressing following buttons: 1, 1, 1
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: N = 7
Output: 9
Explanation: 
We can print at most 9 A's on screen by pressing following buttons:
1, 1, 1, 2, 3, 4, 4
</pre>

Four Button Keyboard

Given two binary strings, return the sum of the two binary strings.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: a = "11", b = "1"
Output: "100"</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: a = "1010", b = "1011"
Output: "10101"</pre>

Binary Addition

Given a positive integer num, continue to add all the digits until the result is a single-digit number. Return that single-digit number.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: <code>38</code> Output: 2 Explanation: First: <code>3 + 8 = 11 Second: </code><code>1 + 1 = 2</code> &nbsp; Return 2, since it is a single-digit number.</pre>
Challenge: Solve it in O(1) time complexity.

Sum Digits

Given 2 non-empty linked lists that represent non-negative integers, add the two numbers and return it as a linked list in reverse order. 

Note: The 2 given linked lists are in reverse order and each linked list node can only store one digit.

Example:

<pre style="white-space: pre-wrap; word-break: keep-all;">
Input: (1 -&gt; 2 -&gt; 3) + (4 -&gt; 5 -&gt; 6)
Output: 5 -&gt; 7 -&gt; 9
Explanation: 321 + 654 = 975.
</pre>

Sum Linked List Numbers

A number sequence is called arithmetic as long as it consists of at least 3 elements and if the difference between any 2 consecutive elements are the same.
For example, these are arithmetic sequences:
<pre style="white-space: pre-wrap; word-break: keep-all;">1, 3, 5, 7, 9
7, 7, 7, 7
3, -1, -5, -9</pre>
The following sequence is not arithmetic.
<pre style="white-space: pre-wrap; word-break: keep-all;">1, 1, 2, 5, 7</pre>
Given an array, A, return the number of arithmetic slices. An arithmetic slice is any pair of integers (P, Q) such that 0 &lt;= P &lt; Q &lt; N and&nbsp;A[P], A[p + 1], ..., A[Q - 1], A[Q] is arithmetic. This means that P + 1 &lt; Q.
&nbsp;
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">A = [1, 2, 3, 4]
</pre>

<pre style="white-space: pre-wrap; word-break: keep-all;">
return: 3 There are 3 arithmetic slices in A: [1, 2, 3], [2, 3, 4] and [1, 2, 3, 4] itself.
</pre>

Count Slices

Implement a calculator that can solve an expression string.
The expression string only contains open and closed parentheses, plus, minus, empty spaces, and non-negative integers only.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "1 + 1"
Output: 2
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: " 2-1 + 2 "
Output: 3</pre>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "(1+(4+5+2)-3)+(6+8)"
Output: 23</pre>
Note:
<ul>
<li>Assume the given expression is always valid.</li>
</ul>

Simple Arithmetic

Given an integer N that is positive, return the maximum distance between any two consecutive 1's in the binary form of N. If two consecutive 1's don't exist then return 0.
<div>
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 22
Output: 2
Explanation: 
The binary form of 22 is: 0b10110.
In the binary representation of 22, there are two consecutive pairs of 1's.
The first consecutive pair of 1's have distance 2 since there is only one 0 in between them.
The second consecutive pair of 1's have distance 1 since there are no 0's between them.
The answer is 2 since the largest distance is 2.
</pre>
<div>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 5
Output: 2
Explanation: 
The binary form of 5 is 0b101.
</pre>
<div>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 6
Output: 1
Explanation: 
The binary form of 6 is 0b110.
</pre>
<div>
Example 4:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 8
Output: 0
Explanation: 
8 in binary is 0b1000.
There are no consecutive 1's so return 0.
</pre>
</div>
</div>
</div>
</div>

Binary Space

We have a stupid calculator that has a number on its display, we can perform two operations:
- Double: double the number on the screen
- Decrement: subtract 1 from the number on the screen
Given X as the initial number on the screen and a number Y, return the minimum number of operations to get from X to Y.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: X = 2, Y = 3
Output: 2
Explanation: Use the double operation and then use the decrement operation {2 -&gt; 4 -&gt; 3}.
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: X = 5, Y = 8
Output: 2
Explanation: Use the decrement operation and then use the double operation {5 -&gt; 4 -&gt; 8}.
</pre>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: X = 3, Y = 10
Output: 3
Explanation: Use the double operation, the decrement operation and then the double operation {3 -&gt; 6 -&gt; 5 -&gt; 10}.
</pre>
Example 4:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: X = 1024, Y = 1
Output: 1023
Explanation: Use decrement operation 1023 times.
</pre>
&nbsp;
Note:
<ol>
<li><code>1 &lt;= X &lt;= 10^9</code></li>
<li><code>1 &lt;= Y &lt;= 10^9</code></li>
</ol>

Stupid Calculator

In a room with n number of lights turned on and 4 buttons on the wall, you perform m number of unknown operations on the buttons. Return how many different kinds of status of the n lights could be.
The n lights are labeled as [1, 2, 3 ..., n], the functionionality of these 4 buttons are given below:
<ol>
<li>Flip all the lights.</li>
<li>Flip lights with even numbers.</li>
<li>Flip lights with odd numbers.</li>
<li>Flip lights with (3k + 1) numbers, k = 0, 1, 2, ...</li>
</ol>
&nbsp;
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: n = 1, m = 1.
Output: 2
Explanation: After 2 operations the lights can be: [on], [off]
</pre>
&nbsp;
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: n = 2, m = 1.
Output: 3
Explanation: After 3 operations the lights can be: [on, off], [off, on], [off, off]
</pre>
&nbsp;
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: n = 3, m = 1.
Output: 4
Explanation: After 2 operations the lights can be: [off, on, off], [on, off, on], [off, off, off], [off, on, on].
</pre>
&nbsp;
Note: <code>n</code> and <code>m</code> both fit in range [0, 1000].

Switch Lights II

Given n representing the number of light bulbs. You follow a sequence of n moves.
The first move you turn all the bulbs on.
The second turn you turn on every second bulb.
The third turn you turn on every third bulb.
...
For every i-th turn you turn on every i-th bulb until you reach the n-th turn where you only turn off the last light bulb.&nbsp;
Return how many light bulbs are on after the n turns.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 3
Output: 1 
Explanation: 
All bulbs are off initially [off, off, off].
After round 1, the light bulbs are: [on, off, on].
After round 2, the light bulbs are: [on, on, on].
After round 3, the light bulbs are: [on, off, off]. 

Return 1 at the end of the n=3 turns.
</pre>

Switch Lights

Given a list of integers and a target integer called k, return true if the array has a continuous subarray that has at least 2 elements and sums up to a multiple of k.&nbsp;
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [23, 2, 4, 6, 7], k=6
Output: True
Explanation: Because [2, 4] is a continuous subarray of size 2 and sums up to 6.
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [23, 2, 6, 4, 7], k=6
Output: True
Explanation: [23, 2, 6, 4, 7] is a continuous subarray of size 5 and sums up to 42 which is a multiple of 6.
</pre>
&nbsp;

Contiguous Array Sum

Given a non-negative integer, n, return the count of prime numbers less than n.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 9
Output: 4
Explanation: The prime numbers less than 9 are: 2, 3, 5, 7.
</pre>

Number Of Primes

Given two integers: a dividend and divisor, return the quotient of the two integers. You cannot use multiplication, division and the mod operator.
The integer division should round toward zero.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: dividend = 11, divisor = 3
Output: 3</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: dividend = 8, divisor = -3
Output: -2</pre>
Note:
<ul>
<li>The input values will be 32-bit signed integers.</li>
<li>You can assume the divisor will never be 0.</li>
<li>If the division result overflows return&nbsp;231 &minus; 1.</li>
</ul>

Integer Division

A derangement is a permutation of a set of elements such that no element appears in the original position.
Given an integer n representing an array consisting of integers from 1 to n in ascending order, return the number of derangements that it can generate mod 109 + 7 since the answer can be large.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 3
Output: 2
Explanation: The original array is [1,2,3]. There are two derangements: [2,3,1] and [3,1,2].
</pre>

Count Derangements

Given a non-negative integer return it as an English word representation.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 123
Output: "One Hundred Twenty Three"
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 12345
Output: "Twelve Thousand Three Hundred Forty Five"</pre>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 1234567
Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"
</pre>
Example 4:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 1234567891
Output: "One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One"
</pre>

Number To Word

Given an integer, return the roman numeral conversion of it. The input is between 1 and 3999.
Roman numerals are represented by 7 different symbols. Here are the symbols and their corresponding integer value:
<pre style="white-space: pre-wrap; word-break: keep-all;">Symbol Value
I 1
V 5
X 10
L 50
C 100
D 500
M 1000</pre>
Example: Two is written as II. Twelve is written as XII. Twenty-seven is written as XXVII.
Roman numerals are written largest to smallest from left to right. However, there are edge cases. The roman numeral for four is not <code>IIII</code>. Instead, the number four is written as <code>IV</code>. This is because we subtract one from the five symbol. The same case applies to the number nine, which is written as <code>IX</code>. There are six cases when subtraction is used to create the roman numeral:
<ul>
<li><code>I</code> can be placed before <code>V</code> (5) and <code>X</code> (10) to make 4 and 9.&nbsp;</li>
<li><code>X</code> can be placed before <code>L</code> (50) and <code>C</code> (100) to make 40 and 90.&nbsp;</li>
<li><code>C</code> can be placed before <code>D</code> (500) and <code>M</code> (1000) to make 400 and 900.</li>
</ul>
&nbsp;
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:&nbsp;3
Output: "III"</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:&nbsp;4
Output: "IV"</pre>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:&nbsp;9
Output: "IX"</pre>
Example 4:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:&nbsp;58
Output: "LVIII"
Explanation: L = 50, V = 5, III = 3.
</pre>
Example 5:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:&nbsp;1994
Output: "MCMXCIV"
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.</pre>

Roman Conversion

Given an array consisting of only positive lengths, return the largest perimeter of a triangle that can be formed from any 3 lengths.
If no triangle can be formed return 0.
<div>
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [2,1,2]
Output: 5
</pre>
<div>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [1,2,1]
Output: 0
</pre>
<div>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [3,2,3,4]
Output: 10
</pre>
<div>
Example 4:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [3,6,2,3]
Output: 8
</pre>
</div>
</div>
</div>
</div>

Largest Surrounding Triangle

Given an integer array, find three numbers whose product is maximum and output the maximum product.
Given an array of integers, return the maximum product between any 3 numbers in the array.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [1,2,3]
Output: 6
</pre>
&nbsp;
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [1,2,3,4]
Output: 24
</pre>
&nbsp;
Constraints:
<ol>
<li>The size of the given array is in range [3,104] and each element is in the range [-1000, 1000].</li>
<li>Multiplying any three numbers in the given array will not exceed the range of a 32-bit signed integer.</li>
</ol>
&nbsp;

Max Product Of Three

Given a positive integer, you can swap any two digits at most once to make a maximum valued number. Return the maximum number you can create.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 2736
Output: 7236
Explanation: Swap digits 2 and 7.
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 9973
Output: 9973
Explanation: No swap.
 </pre>

Largest Swap Number

Given an integer, a that is positive, return the lowest positive integer b when you multiply every digit of b you get a.
If there is no result then return 0.
Example 1 Input:
<pre style="white-space: pre-wrap; word-break: keep-all;">48 </pre>
Output:
<pre style="white-space: pre-wrap; word-break: keep-all;">68</pre>
Example 2 Input:
<pre style="white-space: pre-wrap; word-break: keep-all;">15</pre>
Output:
<pre style="white-space: pre-wrap; word-break: keep-all;">35</pre>

Lowest Factor

Given an array of integers that is not empty, return the minimum number of operations such that all elements in the array are equal. An operation is defined as incrementing or decrementing an element by 1.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:
[1,2,3]

Output:
2

Explanation:
Only two operations are needed (An operation allows you to increment or decrement one element):

[1,2,3] =&gt; [2,2,3] =&gt; [2,2,2]
</pre>

Minimum Moves To Equal Array

Given an integer array of length n where n &gt; 0, return the minimum number of steps to make all elements in the array equal. A step is considered incrementing n - 1 elements by 1.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:
[1,2,3]

Output:
3

Explanation:
Only three steps are required (remember each step increments two (n-1) elements):

[ 1,2,3 ] =&gt; [2,3,3] =&gt; [3,4,3] =&gt; [4,4,4]
</pre>

Minimum Moves To Equate Array

Given an array that consists of n distinct integers taken from [0, 1, ..., n] with one value missing, return the missing integer from the array.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [3,0,1]
Output: 2
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [9,6,4,2,3,5,7,0,1]
Output: 8
</pre>
Challenge: Implement your solution in O(n) time complexity and O(1) space complexity.

Absent Integer

Given an integer n, return the total number of times the digit 1 appears in all non-negative less than or equal to n.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 13
Output: 6 
Explanation: 1 occurrs in these following numbers: 1, 10, 11, 12, 13.
</pre>

Count One Digit

There are a group of <code>N</code> rabbits. <code>S</code> rabbits are chosen where <code>S</code> is between 0 and <code>N</code> inclusive. Each one of the <code>S</code> rabbits tells you how many other rabbits have the same color. The <code>answers</code> are stored in an array.

Return the minimum possible of rabbits that satisfy the given array of <code>answers.</code>

<pre style="white-space: pre-wrap; word-break: keep-all;">
Examples:
Input: answers = [1, 2, 2]
Output: 5
Explanation:
Suppose the one rabbit that answered &quot;1&quot; is colored yellow.
That means that there is an additional yellow rabbit that didn't get chosen to be questioned and recorded in the answers array.
The two rabbits that answered &quot;2&quot; can&#39;t be yellow or the answers wouldn't make sense.
Suppose both the rabbits that answered &quot;2&quot; are green.
Then there should be 1 other green rabbit that wasn&#39;t chosen to be questioned and recorded in the answers array.
Therefore the minimum number of rabbits in the group is 5: 3 that answered plus 2 that didn&#39;t.

Input: answers = [20, 20, 20]
Output: 21

Input: answers = [1, 0, 1, 0, 0]
Output: 5

Input: answers = []
Output: 0
</pre>

Minimum Number Of Rabbits

Imagine standing at position 0 on an infinite timeline. The goal is at index:&nbsp;<code>target</code>. Each step you must go left or right and for each n-th move, you must make n number of steps.&nbsp;
Ex: You must make 1 step during move 1, 2 steps during move 2, etc.
Return the minimum number of moves to reach the target goal.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: target = 3
Output: 2
Explanation:
1st move, step from 0 to 1.
2nd move, step from 1 to 3.
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: target = 2
Output: 3
Explanation:
1st move, step from 0 to 1.
2nd move, step from 1 to -1.
3rd move, step from -1 to 2.
</pre>
Note:
<ul>
<li><code>target</code>&nbsp;is a non-zero integer in the range of&nbsp;<code>[-10^9, 10^9]</code>.</li>
</ul>
&nbsp;

Infinite Timeline

Given a 32-bit signed integer, return the digits in reverse order of the integer.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 123
Output: 321
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: -123
Output: -321
</pre>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 120
Output: 21
</pre>
Note: We are dealing with an environment that can only store integers within the 32-bit signed integer range: [&minus;231,&nbsp; 231&nbsp;&minus; 1]. Assume that your function returns 0 when the reversed integer overflows.

Integer Reversal

Given an array of integers A and another integer K, for each integer in A, we will add a value x to A[i] such that -K &lt;= x &lt;= K.
Once we add the x value to each element in A we have a resulting array, B. Return the smallest possible difference between the max value of B and the min value of B.
<div>
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: A = [1], K = 0
Output: 0
Explanation: B = [1], only one value so return 0
</pre>
<div>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: A = [0,10], K = 2
Output: 6
Explanation: B = [2,8], max value - min value = 8 - 2 = 6
</pre>
<div>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: A = [1,3,6], K = 3
Output: 0
Explanation: B = [3,3,3] or B = [4,4,4], all the same values so return 0
</pre>
&nbsp;
Note:
<ol>
<li><code>1 &lt;= A.length &lt;= 10000</code></li>
<li><code>0 &lt;= A[i] &lt;= 10000</code></li>
<li><code>0 &lt;= K &lt;= 10000</code></li>
</ol>
</div>
</div>
</div>

Minimum Range I

Given an array of integers A and another integer K, for each integer in A, we will add a value x to A[i] such that x = -K or x = K.
Once we add the x value to each element in A we have a resulting array, B. Return the smallest possible difference between the max value of B and the min value of B.
<div>
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: A = [1], K = 0
Output: 0
Explanation: B = [1], only one value return 0
</pre>
<div>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: A = [0,10], K = 2
Output: 6
Explanation: B = [2,8], max - min = 8 - 2 = 6
</pre>
<div>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: A = [1,3,6], K = 3
Output: 3
Explanation: B = [4,6,3], max - min = 6 - 3 = 3
</pre>
&nbsp;
Note:
<ol>
<li><code>1 &lt;= A.length &lt;= 10000</code></li>
<li><code>0 &lt;= A[i] &lt;= 10000</code></li>
<li><code>0 &lt;= K &lt;= 10000</code></li>
</ol>
</div>
</div>
</div>

Minimum Range II

Given a string that represents an equation, return the value of x in the form of x={value}. The equation only contains "+", "-" operations, and the variable x with coefficients.
If no solution exists in the equation, return "No solution".
If there are infinite solutions in the equation, return "Infinite solutions".
If there is exactly one solution for the equation, you can assume the value of <code>x</code> is an integer.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "x+5-3+x=6+x-2"
Output: "x=2"
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "x=x"
Output: "Infinite solutions"
</pre>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "2x=x"
Output: "x=0"
</pre>
Example 4:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "2x+3x-6x=x+2"
Output: "x=-1"
</pre>
Example 5:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "x=x+2"
Output: "No solution"
</pre>

Evaluate Equation

Given an integer, x, return the square root of x rounded down to the nearest integer.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 4
Output: 2
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 8
Output: 2
Explanation: The square root of 8 is 2.82842 so round down to 2 and return it.
</pre>

Square Root

A strobogrammatic number is any number that is the same when it is rotated 180 degrees.
Given an integer n, return all strobogrammatic numbers that have length n.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: n = 2
Output: <code>["11","69","88","96"]</code></pre>

Flipped Number II

Given a low number and a high number as strings return the number of strobogrammatic numbers in that range (inclusive). A strobogrammatic number is any number that is the same when it is rotated 180 degrees.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: low = "50", high = "100"
Output: 3 
Explanation: 69, 88, and 96 are the 3 strobogrammatic numbers.</pre>
&nbsp;

Flipped Number III

A strobogrammatic number is any number that is the same when it is rotated 180 degrees.
Given a number in the form of a string, return true if it's a strobogrammatic number otherwise return false.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "69"
Output: true
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "88"
Output: true</pre>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "962"
Output: false</pre>

Flipped Number

You are given an integer k which represents K number of eggs and an integer N which represents the number of floors in a building.
You want to find out the highest floor such that an egg won't break at that floor. For each move, you are allowed to drop an egg from any floor between 1 to N, if an egg breaks then you cannot drop it anymore.&nbsp;
Return the minimum number of moves to determine the highest floor such that an egg dropped will not break.
<div>
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: K = 1, N = 2
Output: 2
Explanation: 
Drop the egg from floor 1. If it breaks, we know with certainty that the first floor will break the egg.
If it doesn't break, drop the egg from floor 2. If it breaks, we know with certainty that the seccond floor will break the egg.
If it didn't break, then we know that the second floor won't break the egg.
So we return 2 because in the worst case we need 2 moves to find out the max height an egg can be dropped from without breaking.
</pre>
<div>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: K = 2, N = 6
Output: 3
</pre>
<div>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: K = 3, N = 14
Output: 4
</pre>
</div>
</div>
</div>

Dropping Eggs

Given a string, return true if the string can be a valid number.
Examples: <code>"0"</code> =&gt; <code>true</code> <code>" 0.1 "</code> =&gt; <code>true</code> <code>"abc"</code> =&gt; <code>false</code> <code>"1 a"</code> =&gt; <code>false</code> <code>"2e10"</code> =&gt; <code>true</code> <code>" -90e3&nbsp; &nbsp;"</code> =&gt; <code>true</code> <code>" 1e"</code> =&gt; <code>false</code> <code>"e3"</code> =&gt; <code>false</code> <code>" 6e-1"</code> =&gt; <code>true</code> <code>" 99e2.5&nbsp;"</code> =&gt; <code>false</code> <code>"53.5e93"</code> =&gt; <code>true</code> <code>" --6 "</code> =&gt; <code>false</code> <code>"-+3"</code> =&gt; <code>false</code> <code>"95a54e53"</code> =&gt; <code>false</code>
Here are valid characters in a decimal number:
<ul>
<li>Numbers 0-9</li>
<li>Exponent - "e"</li>
<li>Positive/negative sign - "+"/"-"</li>
<li>Decimal point - "."</li>
</ul>
Remember that the context of this matters and that this problem is meant to be ambiguous so that you can carefully gather the specifications and implement a complete solution.

Problem Title	Difficulty	Frequency in Interviews
Sum Linked List Numbers	Medium
Number To Word	Hard
Integer Reversal	Easy
Simple Arithmetic	Hard
Binary Addition	Easy
Roman Conversion	Medium
Number Of Primes	Easy
Absent Integer	Easy
Valid Number	Hard
Square Root	Easy
Integer Division	Medium
Contiguous Array Sum	Medium
Dropping Eggs	Hard
Flipped Number II	Medium
Max Product Of Three	Easy
Minimum Moves To Equate Array	Easy
Switch Lights	Medium
Sum Digits	Easy
Count One Digit	Hard
Flipped Number	Easy
Largest Swap Number	Medium
Flipped Number III	Hard
Evaluate Equation	Medium
Largest Surrounding Triangle	Easy
Count Slices	Medium
Minimum Range I	Easy
Minimum Moves To Equal Array	Medium
Infinite Timeline	Easy
Switch Lights II	Medium
Minimum Number Of Rabbits	Medium
Binary Space	Easy
Stupid Calculator	Medium
Four Button Keyboard	Medium
Count Derangements	Medium
Lowest Factor	Medium
Minimum Range II	Medium

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