LeetCode75——Day23

一、题目

2352. Equal Row and Column Pairs

Given a 0-indexed n x n integer matrix grid, return the number of pairs (ri, cj) such that row ri and column cj are equal.

A row and column pair is considered equal if they contain the same elements in the same order (i.e., an equal array).

Example 1:

Input: grid = [[3,2,1],[1,7,6],[2,7,7]]
Output: 1
Explanation: There is 1 equal row and column pair:

• (Row 2, Column 1): [2,7,7]
  Example 2:

Input: grid = [[3,1,2,2],[1,4,4,5],[2,4,2,2],[2,4,2,2]]
Output: 3
Explanation: There are 3 equal row and column pairs:

• (Row 0, Column 0): [3,1,2,2]
• (Row 2, Column 2): [2,4,2,2]
• (Row 3, Column 2): [2,4,2,2]

Constraints:

n == grid.length == grid[i].length
1 <= n <= 200
1 <= grid[i][j] <= 105

二、题解

使用map保存键值对（vector作为key，该数组的数目作为值），map底层禹unordered_map不同，基于红黑树

class Solution {
public:
    int equalPairs(vector<vector<int>>& grid) {
        int n = grid.size();
        map<vector<int>,int> map;
        //添加行
        for(int i = 0;i < n;i++){
            map[grid[i]]++;
        }
        int res = 0;
        for(int j = 0;j < n;j++){
            //添加列
            vector<int> arr;
            for(int i = 0;i < n;i++){
                arr.push_back(grid[i][j]);
            }
            //如果存在对应的行与其相等，加上对应的行的数目
            if(map.find(arr) != map.end()) res += map[arr];
        }
        return res;
    }
};