题目描述：

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.

代码实现：

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