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Leetcode
Medium
Trees
Recursion
Sum Of Left Leaves
Given a binary tree, compute the sum of all left leaf nodes.
Acceptance 0%
Problem Statement
Problem
You are given the root of a binary tree. A leaf is a node with no children. A left leaf is a leaf node that is the left child of its parent.
Return the sum of all left leaves in the tree.
Notes
- The root itself is not considered a left leaf.
- If the tree has no left leaves, return
0.
Intuition
This is a tree traversal problem where you need to keep track of whether the current node was reached as a left child.
Input Format
- A binary tree root node is provided.
- The tree is represented in standard level-order form when serialized for testing.
Output Format
- Return a single integer: the sum of all left leaf node values.
Constraints
- The number of nodes is non-negative and fits within typical interview constraints.
- Node values may be negative or positive integers.
- The answer fits in a 32-bit signed integer.
Examples
Sample cases returned by the problem API.
Example 1
Input
root = [3,9,20,null,null,15,7]
Output
24
Explanation
The left leaves are 9 and 15. Their sum is 24.
Example 2
Input
root = [1]
Output
0
Explanation
The root is not a left leaf, and there are no other nodes.
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