112 Path Sum

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.

Example：

image.png

Note：

A leaf is a node with no children.

解释下题目：

找出一个从根到叶子节点的路，使这条路上的所有的数字和是sum

1. 递归

实际耗时：1ms

public boolean hasPathSum(TreeNode root, int sum) {
        if (root == null) {
            return false;
        }
        if (root.left == null && root.right == null && sum - root.val == 0) {
            return true;
        }

        return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);
    }

  思路就是递归，简单的一匹。

时间复杂度O(n)

空间复杂度O(1)