250. Count Univalue Subtrees

Posted 2020-10-15 jxr041100

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

 

return 4.

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int countUnivalSubtrees(TreeNode* root) {
        count = 0;
        dfs(root);
        return count;
    }
    
private:
    int count;
    int dfs(TreeNode*root)
    {
        if(!root) return INT_MAX;
        int left = dfs(root->left);
        int right = dfs(root->right);
        
        if(left==INT_MAX&&right==INT_MAX){count++;return root->val;}
        else if(left==INT_MAX || right==INT_MAX)
        {
            if(root->val == left || root->val == right){count++;return root->val;}
            else return INT_MIN;
        }
        else
        {
            if(root->val==left&&root->val==right){count++;return root->val;}
            else return INT_MIN;
        }
    }
};