[leetcode]250. Count Univalue Subtrees统计节点值相同的子树

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 5 Output: 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 }

 

转载于:https://www.cnblogs.com/liuliu5151/p/9171274.html