1. 题目

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.

2. 思路

左右子树各自相等，根节点相等。递归。

3. 代码

/**
 * 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 == NULL && q == NULL) { return true; }
        if (p == NULL || q == NULL) { return false; }
        return p->val == q->val && isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
    }
};