偏移量

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 20;

int Map[N][N], n;
int dx[4] = {1, 0, -1, 0}, dy[4] = {0, -1, 0, 1}, idx;

int main()
{
    cin >> n;
    
    int x = 0, y = n - 1;
    int nex = x, ney = y;
    for (int i = 1; i <= n * n; i ++) {
        Map[x][y] = i;
        
        nex = x + dx[idx];
        ney = y + dy[idx];
        
        if (nex >= n || ney >= n || nex < 0 || ney < 0 || Map[nex][ney]) {
            idx = (idx + 1) % 4;
            nex = x + dx[idx];
            ney = y + dy[idx];
        }
        
        x = nex, y = ney;
        
        // cout << x << ' ' << y << endl;
    }
    
    for (int i = 0; i < n; i ++) {
        for (int j = 0; j < n; j ++) {
            cout << Map[i][j] << ' ';
        }
        cout << endl;
    }
    
    return 0;
}