题解 | #回型矩阵#

核心在于数字增长规律，从左到右，从右往下，从右往左，从下往上，分别控制列、行固定，再实现数字增长。输出完每一层边界后，边界值要对应变化。

#include <iostream>
using namespace std;

int main()
{
    int n = 0;
    cin >> n;
    int arr[20][20] = { 0 };
    int num = 1;
    int top = 0;int bottom = n - 1;
    int left = 0;int right = n - 1;
    while (num <= n * n)
    {
    	//上，左到右，i-列
        for (int i = left;i <= right && (num <= n * n);i++)
        {
            arr[top][i] = num++;
        }
        top++;
    	//右，上到下，i-行
        for (int i = top;i <= bottom && (num <= n * n);i++)
        {
            arr[i][right] = num++;
        }
        right--;
		//下，右到左，i-列
        for (int i = right;i >= left && (num <= n * n);i--)
        {
            arr[bottom][i] = num++;
        }
        bottom--;
		//左，下到上，i-行
        for (int i = bottom;i >= top && (num <= n * n);i--)
        {
            arr[i][left] = num++;
        }
        left++;

    }
		//打印
    for (int i = 0;i < n;i++)
    {
        for (int j = 0;j < n;j++)
        {
            cout << arr[i][j] << " ";
        }
        cout << endl;
    }
    return 0;
}