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.
递归
bool isSameTree(struct TreeNode *p, struct TreeNode *q) {
if (p == NULL)
return q == NULL;
if (q == NULL)
return false;
if (p->val != q->val)
return false;
return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
}