[LeetCode] Path Sum

Problem:

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.

Solution:O(n)

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