[leetcode]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.

算法思路：

dfs

代码如下：

 1 public class Solution {
 2     public boolean hasPathSum(TreeNode root, int sum) {
 3         if(root == null) return false;
 4         if(root.left == null && root.right == null && root.val == sum) return true;
 5         if(root.left != null && hasPathSum(root.left, sum - root.val)) return true;
 6         if(root.right != null && hasPathSum(root.right, sum - root.val)) return true;
 7         return false;
 8     
 9     }
10 }