112.path sum

QUESTION:

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.

EXPLANATION:

就是迭代查看，一直减到最后看看是否等于0.

SOLUTION:

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;
        boolean left = hasPathSum(root.left,sum-root.val);
        boolean right = hasPathSum(root.right,sum - root.val);
        return left || right;
    }
>
--> return <--