Given two binary trees, write a function to check if they are equal or not.
Two binary trees are considered equal if they are structurally identical and the nodes have the same value.
bool isSameTree(TreeNode *p, TreeNode *q) { if(p == NULL || q == NULL) return p == q; else return (p->val == q->val) && isSameTree(p->left, q->left) && isSameTree(p->right,q->right); }