[leetcode] problem 965 – univalued binary tree

public class  {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}

public boolean isUnivalTree(TreeNode root) {
    if (root == null)
        return true;

    if (root.left != null && root.val != root.left.val)
        return false;
    if (root.right != null && root.val != root.right.val)
        return false;
    
    return isUnivalTree(root.left) && isUnivalTree(root.right);
}