[250. Count Univalue Subtrees] #leetcode

250_0824.java

class Solution {
   // O(n) O(n)
    private int count = 0;
    
    public int countUnivalSubtrees(TreeNode root) {
        unival(root, 0);
        return count;    
    }
    
    private boolean unival(TreeNode node, int val) {
        if (node == null) return true;
        if (!unival(node.left, node.val) | !unival(node.right, node.val)) {
            return false;
        }
        count++;
        return node.val == val;
    }
}