[面试算法题]比较二叉树异同-leetcode学习之旅（5）

问题描述

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.

和Balanced Binary Tree那题很像。定义T(p)为以p为根的树，T(p) = T(q)需要符合两个条件：

(1) p和q等价，这里的等价有两种情况：p = q = NULL，或p、q都不为NULL且p->val = q->val。反过来说当p和q中只有一个为NULL，或者p->val != q->val时p和q不等价。

(2) 如果p和q都不为NULL，则要求T(p->left) = T(q->left)且T(p->right) = T(q->right)。

想清楚以上两点，基本上就秒杀了。

c++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 && !q) return true;
        if((!p && q) || (p && !q)) return false;
        if(p->val != q->val) return false;
        return isSameTree(p->left,q->left) && isSameTree(p->right,q->right);
    }
};