[LeetCode]--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.

For example:
Given the below binary tree and sum = 22,

          5
         / \
        4   8
       /   / \
      11  13  4
     /  \      \
    7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

public boolean hasPathSum(TreeNode root, int sum) {
        if (root == null)
            return false;
        //这个判断包含了叶子节点的含义在里面
        if (root.left == null && root.right == null)
            return sum == root.val;
        return hasPathSum(root.left, sum - root.val)
                || hasPathSum(root.right, sum - root.val);
    }

思来想去还是递归最为简便。其他的非递归我也想不出来。