LeetCode-Count Univalue Subtrees

Posted 2020-08-09 LiBlog

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.

Solution:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public class UniValueCount {
        int value;
        boolean isUniValue;
        int count;
        public UniValueCount(int v, boolean is, int num){
            value = v;
            isUniValue = is;
            count = num;
        }
    }
    public int countUnivalSubtrees(TreeNode root) {
        UniValueCount res = countUnivalRecur(root);
        return res.count;
    }
    
    public UniValueCount countUnivalRecur(TreeNode cur){
        if (cur==null){
            return new UniValueCount(0,false,0);
        }
        if (cur.left==null && cur.right==null){
            return new UniValueCount(cur.val,true,1);
        }
        
        UniValueCount res = new UniValueCount(0,true,0);
        if (cur.left!=null){
            UniValueCount leftRes = countUnivalRecur(cur.left);
            res.isUniValue = res.isUniValue && (leftRes.isUniValue && cur.val==leftRes.value);
            res.count += leftRes.count;
        }
        if (cur.right!=null){
            UniValueCount rightRes = countUnivalRecur(cur.right);
            res.isUniValue = res.isUniValue && (rightRes.isUniValue && cur.val==rightRes.value);
            res.count += rightRes.count;
        }
        if (res.isUniValue){
            res.count++;
            res.value = cur.val;
        }
        return res;
    }
}