Path Sum

Easy

DFS

Given the root of a binary tree and an integer targetSum, return true if the tree has a root-to-leaf path such that adding up all the values along the path equals targetSum.

A leaf is a node with no children.

Example Tree:

        5
       / \
      4   8
     /   / \
    11  13  4
   /  \      \
  7    2      1

Target Sum: 22 Result: true (path 5 -> 4 -> 11 -> 2 = 22)

Key Insight: Use DFS to explore all root-to-leaf paths. At each step, subtract the current node's value from the target. If we reach a leaf node where the remaining target equals the node's value, we found a valid path.

Example 1

Input: root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22

Output: true

Explanation: The path 5 -> 4 -> 11 -> 2 sums to 22.

Example 2

Input: root = [1,2,3], targetSum = 5

Output: false

Explanation: Paths are 1->2 (sum=3) and 1->3 (sum=4). Neither equals 5.

Example 3

Input: root = [], targetSum = 0

Output: false

Explanation: Empty tree has no paths, so no path sum can equal any target.

Constraints

•The number of nodes in the tree is in the range [0, 5000].
•-1000 <= Node.val <= 1000
•-1000 <= targetSum <= 1000

Show Hints (4)

Hint 1: What defines a valid ending point? It must be a leaf node (no children).

Hint 2: Instead of tracking the sum, try subtracting each node value from the target. When do you know you found a valid path?

Hint 3: At a leaf node, check if the remaining target equals the leaf value.

Hint 4: Remember: paths must go from root to leaf, not stop at internal nodes!

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Test Results

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