Given a simple expression string, return the evaluation of it.
The expression string contains only open ( and closed parentheses),&nbsp;non-negative&nbsp;integers, + sign, - sign, * sign, / sign, and empty spaces. The integer division should always truncate towards 0.
You can always assume a valid string.
Some examples:
<pre style="white-space: pre-wrap; word-break: keep-all;">"1 + 1" = 2
" 6-4 / 2 " = 4
"2*(5+5*2)/3+(6/2+8)" = 21
"(2+6* 3+5- (3*14/7+2)*5)+3"=-12
</pre>
&nbsp;

Simple Calculator III

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 a list of temperatures return the list of temperatures such that each day tells you how many days you need to wait until a day with warmer temperature. If there is no future date with warmer temperature then return 0.
For example, given the list of temperatures <code>T = [73, 74, 75, 71, 69, 72, 76, 73]</code>,&nbsp; output&nbsp;<code>[1, 1, 4, 2, 1, 1, 0, 0]</code>.

Warm Temperatures

There is a single-threaded CPU executing n number of functions. Every function has a unique id between 0 and N-1.
Logs are stored in timestamp order to describe if a function has entered or exited.
Every log line is stored in this format: <code>"{function_id}:{"start" | "end"}:{timestamp}"</code>.&nbsp;
For example:&nbsp;<code>"0:start:3"</code>&nbsp;means the function with id <code>0</code> starts running at timestamp&nbsp;<code>3</code>.&nbsp; <code>"1:end:2"</code> means the function with id <code>1</code> finished running at timestamp <code>2</code>.
A function's exclusive time&nbsp;is the total number of time units spent running.
Return the exclusive time for each function, ordered by their function id.
&nbsp;
Example 1:
<img style="width: auto; height: 150px;" src="https://swecareers-images.s3.us-east-2.amazonaws.com/images/time-functions/diag1b.png" alt="" />
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:
n = 2
logs = ["0:start:0","1:start:2","1:end:5","0:end:6"]
Output: [3, 4]
Explanation: Function 0 started running at timestamp 0 and runs for 2 units. We then switch to function 1 running at timestamp 2 for 4 time units until it stops at the end of timestamp 5. This means the exclusive time for function 1 is 4. Function 0 begins running for 1 time unit at timestamp 6 and ends. Function 0 has an exclusive time of 2 + 1 = 3 since it ran for 2 time units earlier and ends with another 1 time unit.</pre>
&nbsp;
Note:
<ol>
<li>Two functions will never start or end at the same time.</li>
<li>Functions will always have a start and end log.</li>
</ol>
&nbsp;

Time Functions

Given a chemical formula in the form of a string, return the count of each atom in the form of a string that follows this format: the name of the first atom (this must be in sorted ascending order), followed by the count, the name of the second atom, followed by its count and so on.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 
formula = "H2O"
Output: "H2O"
Explanation: 
The count of the atoms are {'H': 2, 'O': 1}.
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 
formula = "Mg(OH)2"
Output: "H2MgO2"
Explanation: 
The count of the atoms are {'H': 2, 'Mg': 1, 'O': 2}.
</pre>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 
formula = "K4(ON(SO3)2)2"
Output: "K4N2O14S4"
Explanation: 
The count of the atoms are {'K': 4, 'N': 2, 'O': 14, 'S': 4}.
</pre>
&nbsp; 
&nbsp;

Count Atoms

You are given a string and are required to remove the duplicate characters in the string such that each character appears once. Return the smallest word that satisfies this condition when arranged in lexicographical order.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: <code>"bcabc"</code> Output: <code>"abc"</code></pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: <code>"cbacdcbc"</code> Output: <code>"acdb"</code></pre>

Delete Repeating Letters

Given a string representing arbitrarily nested ternary expressions, calculate the result of the expression. You can always assume that the given expression is valid and only consists of digits <code>0-9</code>, <code>?</code>, <code>:</code>, <code>T</code> and <code>F</code> (<code>T</code> and <code>F</code> represent True and False respectively).
Given a string that represents an arbitrary number of nested ternary expressions, return the result of the expression.
Constraints:
<ol>
<li>The size of the given string is less than 10000.</li>
<li>Each number contains only one digit.</li>
<li>Assume that the expression is always valid and only contains characters 0 to 9, ?, :, T and F (T and F represent True and False respectively).</li>
<li>The conditional expressions group right-to-left.</li>
<li>The condition will always be&nbsp;<code>T</code> or <code>F</code>. That is, the condition will never be a digit.</li>
<li>The result of the expression will always result in a digit <code>0 to 9</code>, <code>T</code> or <code>F</code>.</li>
</ol>
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "T?2:3"

Output: "2"

Explanation: If true, then result is 2; otherwise result is 3.
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "F?1:T?4:5"

Output: "4"

Explanation: The conditional expressions group right-to-left. Using parenthesis, it is read/evaluated as:

 "(F ? 1 : (T ? 4 : 5))" "(F ? 1 : (T ? 4 : 5))"
 -> "(F ? 1 : 4)" or -> "(T ? 4 : 5)"
 -> "4" -> "4"
</pre>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: "T?T?F:5:3"

Output: "F"

Explanation: The conditional expressions group right-to-left. Using parenthesis, it is read/evaluated as:

 "(T ? (T ? F : 5) : 3)" "(T ? (T ? F : 5) : 3)"
 -> "(T ? F : 3)" or -> "(T ? F : 5)"
 -> "F" -> "F"
</pre>

Parse Ternary Expression

Given an array of non-negative integers that represent elevations in a mountain, return the total amount of water the mountains store after raining.
<img style="width: auto; height: 100px;" src="https://swecareers-images.s3.us-east-2.amazonaws.com/images/water-in-mountains/example-1.png" /> The above mountain is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of water (blue section) are contained.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [0,1,0,2,1,0,1,3,2,1,2,1]
Output: 6</pre>

Water In Mountains

You are given a string with the characters <code>&#39;(&#39;</code>, <code>&#39;)&#39;</code>, <code>&#39;{&#39;</code>, <code>&#39;}&#39;</code>, <code>&#39;[&#39;</code> and <code>&#39;]&#39;</code>, determine if the string has a valid sequence of brackets.

An input string is valid if all brackets are be closed by the same type of brackets and in the correct order.

An empty string is&nbsp;also valid.

Example 1:

<pre style="white-space: pre-wrap; word-break: keep-all;">
Input: &quot;()&quot;
Output: true
</pre>

Example 2:

<pre style="white-space: pre-wrap; word-break: keep-all;">
Input: &quot;()[]{}&quot;
Output: true
</pre>

Example 3:

<pre style="white-space: pre-wrap; word-break: keep-all;">
Input: &quot;(]&quot;
Output: false
</pre>

Example 4:

<pre style="white-space: pre-wrap; word-break: keep-all;">
Input: &quot;([)]&quot;
Output: false
</pre>

Example 5:

<pre style="white-space: pre-wrap; word-break: keep-all;">
Input: &quot;{[]}&quot;
Output: true
</pre>

Validate Brackets

Given an array of integers, return true if it's the correct preorder traversal of a binary search tree.
Assume each integer in the array is unique.
Given this binary search tree:&nbsp;
<pre style="white-space: pre-wrap; word-break: keep-all;"> 5
 / \
 2 6
 / \
 1 3</pre>
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [5,2,6,1,3]
Output: false</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [5,2,1,3,6]
Output: true</pre>
Challenge: Try doing it in O(1) space.
<pre style="white-space: pre-wrap; word-break: keep-all;">&nbsp;</pre>

Problem Title	Difficulty	Frequency in Interviews
Water In Mountains	Hard
Validate Brackets	Easy
Simple Arithmetic	Hard
Simple Calculator III	Hard
Time Functions	Medium
Delete Repeating Letters	Hard
Warm Temperatures	Medium
Count Atoms	Hard
Verify Preorder Sequence In Binary Search Tree	Medium
Parse Ternary Expression	Medium

Most Frequently Asked Stack Interview Questions

Sort By: Company Questions

Sort By: Problem Type