简单题。递归。
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public boolean hasPathSum(TreeNode root, int sum) { // Start typing your Java solution below // DO NOT write main() function if (root == null) { return false; } if (root.left == null && root.right == null) { return root.val == sum; } else { return hasPathSum(root.left, sum-root.val) || hasPathSum(root.right, sum-root.val); } } }