LeetCode 965. Univalued Binary Tree

check if every value on this tree is univalue or not.

using recursion and the equation will be:
isUnivalue(root) = isUnivalue(root.left) && isUnivalue(root.right)
but the problem is we don’t have the value to compare if any one is false.
so I use an extra recursion.

class Solution {
    public boolean isUnivalTree(TreeNode root) {
        if (root == null) return true;
        
        //if root is not null, then it means each value should have the same value as rppt.val
        return isUnivalTree(root, root.val);
    }
    
    private boolean isUnivalTree(TreeNode root, int value) {
        if (root == null) return true;
        
        if (root.val != value) return false;
        
        return isUnivalTree(root.left, value) && isUnivalTree(root.right, value);
    }
}