Path Sum (LeetCode Tree)

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.

Idea: Brute force recursion.

Time: O(n) Space: O(lgn)

Code:

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