112. Path Sum.md

Difficulty	Related Topics	Similar Questions
Easy	Tree Depth-first Search https://leetcode.com/tag/tree https://leetcode.com/tag/depth-first-search	Path Sum II Binary Tree Maximum Path Sum Sum Root to Leaf Numbers Path Sum III Path Sum IV https://leetcode.com/problems/path-sum-ii https://leetcode.com/problems/binary-tree-maximum-path-sum https://leetcode.com/problems/sum-root-to-leaf-numbers https://leetcode.com/problems/path-sum-iii https://leetcode.com/problems/path-sum-iv

112. Path Sum

Problem:

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

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

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

Solution:

Note that node value could be negative so pruning can not be performed.

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} sum
 * @return {boolean}
 */
var hasPathSum = function(root, sum) {
  if (!root) { return false }
  if (root.left === null && root.right === null) { return root.val === sum }
  return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val)
};

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