Same Tree

Given two binary trees, write a function to check if they are equal or not.

• Time: O(N)
• Space: O(1)

public boolean isSameTree(TreeNode p, TreeNode q) {
    if (p == null && q == null) {
        return true;
    }
    if (p == null || q == null) {
        return false;
    }
    return p.val == q.val && isSameTree(p.left, q.left) 
            && isSameTree(p.right, q.right);
}