93: Count univalue subtrees

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

Note: uni-value means all subtree nodes have the same value

 

Example 1

Input:        1  
             / \
            2   3

Output: 2

Explanation: 2 and 3 have the same left and right subtrees

Example 2

Input:     1  
          / \  
         1   1 

Output: 3