java 250.计算Univalue Subtrees.java

Posted 2021-05-08

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int countUnivalSubtrees(TreeNode root) {
        int[] count = new int[] {0};
        isUnivalSubtrees(root,count);
        return count[0];
    }
    
    private boolean isUnivalSubtrees(TreeNode root, int[] count) {
        if(root == null) return true;
        
        boolean left = isUnivalSubtrees(root.left, count);
        boolean right = isUnivalSubtrees(root.right, count);
        if(left && right) {
            if(root.left != null && root.left.val != root.val) {
                return false;
            }
            if(root.right != null && root.right.val != root.val) {
                return false;
            }
            count[0]++;
            return true;
        }
        return false;
    }
}
/*
[]
[5,1,5,5,5,null,5]
[5,1,3,1,1,1]
*/