LeetCode(112)——Path Sum

題目：

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.

Note: A leaf is a node with no children.

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.

AC:

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

遞歸求解，1ms