Daily question-leetcode1260-2d grid migration array mapping

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Note：

Expand into a one-dimensional array , In the question is to put the last K Move the position to the beginning
1、 Entire array flip
2、0 ~ k Flip
3、k ~ n * m Flip
You can achieve the effect , When flipping, you don't have to really expand it into a one-dimensional array , Establish a mapping relationship to swap that will do

The code is as follows ：

class Solution {
    
public:
    int n, m;

    void reverse(vector<vector<int>>& g, int start, int end){
    
        for(int i = start, j = end - 1; i < j; i ++, j --)
            swap(g[i / m][i % m], g[j / m][j % m]);
    }

    vector<vector<int>> shiftGrid(vector<vector<int>>& grid, int k) {
    
        n = grid.size(), m = grid[0].size();
        k %= n * m;
        reverse(grid, 0, n * m);
        reverse(grid, 0, k);
        reverse(grid, k, n * m);
        return grid;
    }
};