Spiral

#include <cstdio>
#include <vector>
#include <cassert>
#include <string>
#include <algorithm>
using namespace std;

const int MAXN = 101;

int a[MAXN][MAXN];
int dx[4] = {0, 1, 0, -1};
int dy[4] = {1, 0, -1, 0};

int main()
{
    int n,m;
    scanf("%d%d",&n,&m);
    int x = 0;
    int y = 0;
    int dir = 0;
    int k = 1;

    a[0][0] = k;
    k++;

    while( k <= n*m )
    {
        int nextX = x + dx[dir];
        int nextY = y + dy[dir];
        if( 0<= nextX && nextX < n && 0<= nextY && nextY < m && a[nextX][nextY] == 0)
        {
            x = nextX;
            y = nextY;
            a[x][y] = k;
            k++;
        }
        else
        {
            dir++;
            if(dir==4)
                dir=0;
        }
    }

    for(int i=0; i<n; i++)
    {
        for(int j=0; j<m; j++)
        {
            if(j!=0)
                printf(" ");
            printf("%d", a[i][j]);
        }
        printf("\n");
    }
    return 0;
}