This problem was asked by Google.

A unival tree (which stands for “universal value”) is a tree where all nodes under it have the same value.

Given the root to a binary tree, count the number of unival subtrees.

For example, the following tree has 5 unival subtrees:

采用bottom-up的递归方法。
Time complexity of this solution is O(n) where n is number of nodes in given binary tree.
Auxiliary Space: O(h) where h is the height of the tree due to recursion call.

#include<bits/stdc++.h>
using namespace std;
 
// A Tree node
struct Node
{
   
    int data;
    struct Node* left, *right;
};
 
// Utility function to create a new node
Node* newNode(int data)
{
   
    Node* temp = new Node;
    temp->data = data<