題目：
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.
C代碼：
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* struct TreeNode *left;
* struct TreeNode *right;
* };
*/
bool isSameTree(struct TreeNode* p, struct TreeNode* q) {
if(p==NULL && q==NULL) return true;
else if(p==NULL || q==NULL) return false;
else return p->val==q->val && isSameTree(p->left,q->left) && isSameTree(p->right,q->right);
}
