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：
class Solution {
int result;
public int countUnivalSubtrees(TreeNode root) {
result = 0;
helper(root);
return result;
}
private boolean helper(TreeNode node){
if(node == null ) return true;
boolean left = helper(node.left);
boolean right = helper(node.right);
if(left&&right){
if ((node.left!= null && node.val != node.left.val) || (node.right!= null && node.val != node.right.val) ){
return false;
}
result++;
return true;
}
return false;
}
}