112. Path Sum （判断路径和是否等于某值）

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.

 1 class Solution {
 2     public boolean hasPathSum(TreeNode root, int sum) {
 3         
 4         if(root==null) return false;
 5         
 6         if (root.left==null && root.right==null && sum-root.val==0) return true;
 7         
 8         return hasPathSum(root.left, sum-root.val) ||hasPathSum(root.right,sum-root.val);
 9         
10     }
11 }