[leetcode] 840. Magic Squares In Grid

Description

A 3 x 3 magic square is a 3 x 3 grid filled with distinct numbers from 1 to 9 such that each row, column, and both diagonals all have the same sum.

Given an grid of integers, how many 3 x 3 “magic square” subgrids are there? (Each subgrid is contiguous).

Example 1:

Input: [[4,3,8,4],
        [9,5,1,9],
        [2,7,6,2]]
Output: 1
Explanation: 
The following subgrid is a 3 x 3 magic square:
438
951
276

while this one is not:
384
519
762

In total, there is only one magic square inside the given grid.

Note:

1. 1 <= grid.length <= 10
2. 1 <= grid[0].length <= 10
3. 0 <= grid[i][j] <= 15

分析

题目的意思是：给你一个矩阵，找出有多少个3*3的magic squares，即对角线，横向，竖向的和都一样。
-这是我们小学的时候填数字的游戏，懂一点的都知道中间必须是5才行，然后横向，竖向，对角线的和都是15.这样编程就容易很多了，直接看代码。

代码

class Solution {
public:
    int numMagicSquaresInside(vector>& grid) {
        int m=grid.size();
        int n=grid[0].size();
        int count=0;
        for(int i=0;i>& grid,int x,int y){
        int pre=15;
        int sum=0;
        //each row
        for(int i=x;i9){
                    return false;
                }
                sum+=grid[i][j];
            }
            if(pre!=sum){
                return false;
            }
        }
        //each column
         for(int j=y;j

参考文献

840. Magic Squares In Grid