题解 | #回型矩阵#

#include <stdio.h>
int main() {
    int arr[20][20], n;
    scanf("%d", &n);
    int up = 0, left = 0, right = n - 1, down = n - 1;
    int x = 1;
    while (x <= n * n) {
        for (int i = left; i <= right; i++) {
            arr[up][i] = x++;
        }
        up++;
        for (int i = up; i <= down; i++) {
            arr[i][right] = x++;
        }
        right--;
        for (int i = right; i >= left; i--) {
            arr[down][i] = x++;
        }
        down--;
        for (int i = down; i >= up; i--) {
            arr[i][left] = x++;
        }
        left++;
    }
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            printf("%d ", arr[i][j]);
        }
        printf("\n");
    }
    return 0;
}