Given a binary tree, count the number of uni-value subtrees.

A Uni-value subtree means all nodes of the subtree have the same value.

Example :

Input:  root = [5,1,5,5,5,null,5]              5             / \            1   5           / \   \          5   5   5Output: 4

 

题意：

给定一棵二叉树，求所有节点都同值的二叉树。

 

思路：

dfs

 

代码：

1 class Solution { 2     int result;  3     public int countUnivalSubtrees(TreeNode root) { 4         result = 0;  5         helper(root);  6         return result; 7     } 8       9     private boolean helper(TreeNode node){10         if(node == null ) return true;11         12         boolean left = helper(node.left);13         boolean right = helper(node.right);14         15         if(left&&right){16         if ((node.left!= null && node.val != node.left.val) || (node.right!= null && node.val != node.right.val) ){17                 return false;18             }19             result++;20             return true;21         } 22         return false;23     }24 }