112.路径总和.ts

/*
 * @lc app=leetcode.cn id=112 lang=typescript
 *
 * [112] 路径总和
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function hasPathSum(root: TreeNode | null, targetSum: number): boolean {
  if (!root) return false;
  let res: boolean = false;
  const dfs = (n, s) => {
    // 当为叶子节点时 
    if (!n.left && !n.right && s === targetSum) res = true
    if (n.left) dfs(n.left, s + n.left.val)
    if (n.right) dfs(n.right, s + n.right.val)
  }
  dfs(root, root.val)

  return res;

};
// @lc code=end