Java concise 8-liner 1ms solution

  • 0
    public class Solution {
        public int countUnivalSubtrees(TreeNode root)  return Math.abs(helper(root)); 
        private int helper(TreeNode root){
            if(null==root) return 0; 
            int l = helper(root.left), r = helper(root.right);
            if(l<0 || r<0 || (null!=root.left && root.val!=root.left.val) || (null!=root.right && root.val!=root.right.val)){
                return -Math.abs(l)-Math.abs(r);
            return l+r+1;

    Helper function returns number of univalue subtrees. Here I used negative numbers to indicate current tree is not a univalue tree. I guess there may be overflow issues, although OJ did not test it.

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