面试题18：如何判断两棵二叉树是否相同？

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.

/**
 * Definition for binary tree
 * 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;
        }else if(p->val == q->val){
            if(isSameTree(p->left,q->left) && isSameTree(p->right,q->right)){
                return true;
            }else{
                return false;
            }
        }else{
            return false;
        }
    }
};