示例 示例 1：
输入：root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22
输出：true示例 2：
输入：root = [1,2,3], targetSum = 5
输出：false
解释：树中存在两条根节点到叶子节点的路径：
(1 --> 2): 和为 3
(1 --> 3): 和为 4
不存在 sum = 5 的根节点到叶子节点的路径。示例 3：
输入：root = [], targetSum = 0
输出：false
解释：由于树是空的，所以不存在根节点到叶子节点的路径。
代码(Java) class Solution {public boolean hasPathSum(TreeNode root, int targetSum) {if (root == null) {return false;}if (root == null) {return false;}if (root.left == null && root.right == null) {return targetSum == root.val;}return hasPathSum(root.left, targetSum - root.val) || hasPathSum(root.right, targetSum - root.val);}public boolean hasPathSum(TreeNode root, int targetSum, int sum) {if (root.left == null && root.right == null) {return (sum + root.val) == targetSum;}boolean left = false;boolean right = false;if (root.left != null) {left = hasPathSum(root.left, targetSum, sum + root.val);}if (root.right != null) {right = hasPathSum(root.right, targetSum, sum + root.val);}return left || right;}
}
