一:题目

二:上码

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {private int sum = 0;private boolean ans = false;public void preOrder(TreeNode root,int targetSum) {if (root == null) return;if (root.left == null && root.right == null) {if (sum == targetSum) {ans = true;}    }if (root.left != null) {//这里没有对root.left的判空 对于 root.left.val;sum += root.left.val;preOrder(root.left,targetSum);sum -= root.left.val;} if (root.right != null) {sum += root.right.val;preOrder(root.right,targetSum);sum -= root.right.val;}}public boolean hasPathSum(TreeNode root, int targetSum) {if (root == null && targetSum == 0) return false;if (root != null) sum = root.val;preOrder(root,targetSum);return ans;}
}