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.
For example:
Given binary tree,
5
/ \
1 5
/ \ \
5 5 5
一刷
題解：注意
5
/ \
5 5
算3棵樹
用DFS的原理蒂誉，和boolean變量保存它的左右是否為univalue subtree.
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
private int count = 0;
public int countUnivalSubtrees(TreeNode root) {
helper(root);
return count;
}
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) return false;
if(node.right!=null && node.val!= node.right.val) return false;
count++;
return true;
}
return false;
}
}
二刷
recursion
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
private int count = 0;
public int countUnivalSubtrees(TreeNode root) {
helper(root);
return count;
}
private boolean helper(TreeNode root){
if(root == null) return true;
boolean left = helper(root.left);
boolean right = helper(root.right);
if(left && right){
if(root.left!=null && root.val != root.left.val) return false;
if(root.right!=null && root.val != root.right.val) return false;
count++;
return true;
}
return false;
}
}
