Given a binary tree return the length of the longest consecutive path.
A path is defined as a sequence of nodes that connects a node with another node along the parent-child connections.
A consecutive path can be either increasing or decreasing but a path such as [1,2,4,3] is invalid.
&nbsp;
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:
 1
 / \
 2 3
Output: 2
Explanation: The longest consecutive path is [1, 2] or [2, 1].
</pre>
&nbsp;
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:
 2
 / \
 1 3
Output: 3
Explanation: The longest consecutive path is [1, 2, 3] or [3, 2, 1].
</pre>
&nbsp;

Binary Tree Longest Consecutive Sequence II

Given a binary tree return the length of the longest consecutive path.
A path is defined as a sequence of nodes that connects a node with another node along the parent-child connections. The longest path must be from a parent to a child and cannot be reversed.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:

 1
 \
 3
 / \
 2 4
 \
 5

Output: <code>3</code> Explanation: The longest consecutive path is <code>3-4-5</code>, so return <code>3</code>.</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:

 2
 \
 3
 / 
 2 
 / 
 1

Output: 2 

Explanation: The longest consecutive path is <code>2-3</code>, not <code>3-2-1</code>, so return <code>2</code>.</pre>

Longest Binary Tree Path

Given a binary tree that is not empty, return the sum of the maximum path. A path of a tree is defined as a sequence of nodes connecting one node to any other node in the tree that flows along the parent-child connections and there must be at the least, one node that doesn't go through the root.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [1,2,3]

 1
 / \
 2 3

Output: 6
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [-10,9,20,null,null,15,7]</pre>

<pre style="white-space: pre-wrap; word-break: keep-all;">
 -10
 / \
 9 20
 / \
 15 7
</pre>
Output: 42

Binary Tree Max Path

Given the root of a binary tree, return the diff of the entire tree.
The diff of a tree is the absolute difference between the sum of the left subtree nodes and the sum of the right subtree nodes. When a node is null, return 0.
The diff of the whole tree is defined as the sum of all nodes' diff.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 
 1
 / \
 2 3
Output: 1
Explanation: 
Diff of node 2 : 0
Diff of node 3 : 0
Diff of node 1 : |2-3| = 1
Diff of entire tree : 0 + 0 + 1 = 1
</pre>

Binary Tree Diff

Given a binary tree, return the count of the number of subtrees containing only the same value.
Example :
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: root = [5,1,5,5,5,null,5]

 5
 / \
 1 5
 / \ \
 5 5 5

Output: 4 Explanation: Count the 3 leaf subtrees and the sub-tree with 5 and a child on the right as 5. </pre>

Number Of Subtrees With Single Value

Given the root of a binary tree, return the diameter of the tree.&nbsp;
A diameter of a tree is defined as the longest path from one node to another node. The path doesn't necessarily have to pass through the root. The length of a path is defined by the number of edges between nodes.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;"> 1
 / \
 2 3
 / \ 
 4 5 
</pre>
Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

Binary Tree Diameter

Given the root of a binary tree, return the leftmost value in the last row of the tree.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:
</pre>
<pre style="white-space: pre-wrap; word-break: keep-all;">
 2
 / \
 1 3
</pre>
<pre style="white-space: pre-wrap; word-break: keep-all;">
Output:
1
</pre>
 Example 2: 
<pre style="white-space: pre-wrap; word-break: keep-all;">Input:

 1
 / \
 2 3
 / / \
 4 5 6
 /
 7

Output:
7
</pre>
You can assume valid input and the root node is not NULL.

Binary Tree Left Most Value

Given a binary tree, return the number of nodes in the largest sub-tree that is also a Binary Search Tree (BST).
Example:

<pre style="white-space: pre-wrap; word-break: keep-all;">
Input: [10,5,15,1,8,null,7]

 10 
 / \ 
 5 15 
 / \ \ 
1 8 7

Output: 3
Explanation: The largest BST sub-tree is the red one, and the number of nodes is 3.
</pre>

Challenge: Can you solve it in O(n) time complexity?

Tree With Largest Bst

Given a binary tree, return the length of the longest path such that each node in the path has the same value. The path doesn't necessarily have to pass through the root. The length of a certain path means the number of edges between the nodes.
&nbsp;
Example 1:
Input:
<pre style="white-space: pre-wrap; word-break: keep-all;"> 5
 / \
 4 5
 / \ \
 1 1 5
</pre>
Output:&nbsp;2
&nbsp;
Example 2:
Input:
<pre style="white-space: pre-wrap; word-break: keep-all;"> 1
 / \
 4 5
 / \ \
 4 4 5
</pre>
Output:&nbsp;2
&nbsp;

Single Number Path

Given a binary tree, return the max depth.
The max depth is the number of nodes from the root node to the deepest leaf node. A leaf node is a node without any children.
Example:
Given binary tree <code>[3,9,20,null,null,15,7]</code>,
<pre style="white-space: pre-wrap; word-break: keep-all;"> 3
 / \
 9 20
 / \
 15 7</pre>
return 3.

Binary Tree Max Depth

Given a binary tree, return the maximum width of the tree. A width of a level of a binary tree is defined as the length between the leftmost and rightmost non-null nodes on that certain level where null nodes are also counted between the two end nodes.&nbsp;
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 

 1
 / \
 3 2
 / \ \ 
 5 3 9 

Output: 4
Explanation: The max width is on the third level between 5 and 9 including the null node.
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 

 1
 / 
 3 
 / \ 
 5 3 

Output: 2
Explanation: The max widhth is on the third level between 5 and 3.
</pre>
Example 3:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 

 1
 / \
 3 2 
 / 
 5 

Output: 2
Explanation: The max width is on the second level between 3 and 2.
</pre>
Example 4:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 

 1
 / \
 3 2
 / \ 
 5 9 
 / \
 6 7
Output: 8
Explanation:The max width is on the fourth level with the length 8 (6,null,null,null,null,null,null,7).

</pre>

Binary Tree Max Width

Given a binary tree, return the minimum depth.
The minimum depth is the shortest path from the root node to a leaf node. A leaf node has no children.
Example:
Given the tree <code>[3,9,20,null,null,15,7]</code>,
<pre style="white-space: pre-wrap; word-break: keep-all;"> 3
 / \
 9 20
 / \
 15 7</pre>
return 2.

Binary Tree Min Depth

When the depth of a tree is less than 5, the tree can be represented as a list of three-digit integers.
For every integer in the list:
<ol>
<li>The hundreds digit represents the depth of where the node lives, <code>1 &lt;= D &lt;= 4.</code></li>
<li>The tens digit represents the position <code>P</code> of the node in the current level, it belongs to, <code>1 &lt;= P &lt;= 8</code>. The position is the same as that in a full binary tree.</li>
<li>The one's digit represents the value <code>V</code> of this node, <code>0 &lt;= V &lt;= 9.</code></li>
</ol>
Given a list of ascending three-digit integers, return the sum of all paths from the root node to the leaf nodes.
Example 1:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [113, 215, 221]
Output: 12
Explanation: 
The tree that the list represents is:
 3
 / \
 5 1

The path sum is (3 + 5) + (3 + 1) = 12.
</pre>
Example 2:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [113, 221]
Output: 4
Explanation: 
The tree that the list represents is: 
 3
 \
 1

The path sum is (3 + 1) = 4.
</pre>

Sum Of Paths IV

Given a binary tree, each node only has a value from 0 to 25 that represent the lowercase letters 'a' to 'z'. 0 represents 'a', 1 represents 'b' and so on until 25 represents 'z'.
Return the lexicographically smallest string that can be formed from a leaf to the root of the binary tree.
Note: A short prefix of a string is lexicographically smaller than the whole string. For example "ab" is lexicographically smaller than "aba". Also, a leaf of a node is a node without any children.
<div>
<div>
&nbsp;
</div>
</div>
<div>
Example 1:
<img style="width: 100px; height: auto;" src="https://swecareers-images.s3.us-east-2.amazonaws.com/images/smallest-string-in-tree/example-1.png" alt="" />
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [0,1,2,3,4,3,4]
Output: "dba"
</pre>
<div>
Example 2:
<img style="width: 100px; height: auto;" src="https://swecareers-images.s3.us-east-2.amazonaws.com/images/smallest-string-in-tree/example-2.png" alt="" />
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [25,1,3,1,3,0,2]
Output: "adz"
</pre>
<div>
Example 3:
<img style="height: 100px; width: auto;" src="https://swecareers-images.s3.us-east-2.amazonaws.com/images/smallest-string-in-tree/example-3.png" alt="" />
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: [2,2,1,null,1,0,null,0]
Output: "abc"
</pre>
&nbsp;
</div>
</div>
</div>

Smallest String In Tree

Given an integer&nbsp;n, return the number of structurally distinct binary search trees that can be created where the values store 1 .. n.
Example:
<pre style="white-space: pre-wrap; word-break: keep-all;">Input: 3
Output: 5
Explanation:
Given n = 3, you can create 5 structurally distinct BST's:

 1 3 3 2 1
 \ / / / \ \
 3 2 1 1 3 2
 / / \ \
 2 1 2 3
</pre>

Distinct Binary Search Trees

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
Binary Tree Max Path	Hard
Binary Tree Diameter	Easy
Number Of Subtrees With Single Value	Medium
Binary Tree Max Depth	Easy
Distinct Binary Search Trees	Medium
Tree With Largest Bst	Medium
Verify Preorder Sequence In Binary Search Tree	Medium
Binary Tree Max Width	Medium
Longest Binary Tree Path	Medium
Binary Tree Left Most Value	Medium
Binary Tree Longest Consecutive Sequence II	Medium
Single Number Path	Easy
Binary Tree Min Depth	Easy
Binary Tree Diff	Easy
Sum Of Paths IV	Medium
Smallest String In Tree	Medium

Most Frequently Asked Tree Interview Questions

Sort By: Company Questions

Sort By: Problem Type