A Knight's Journey （DFS）

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<set>
#include<vector>
#include<stack>
#include<queue>
#include<algorithm>
#include<cstdio>
#include<algorithm>
#include<functional>
#include<sstream>
int n1, n2;
int xx[30], yy[30];
int visit[30][30];
int flag;
int dir[8][2] = { { -2,-1 },{ -2,1 },{ -1,-2 },{ -1,2 },{ 1,-2 },{ 1,2 },{ 2,-1 },{ 2,1 } };
int go(int x, int y)
{
    if (1 <= x&&x <= n1 && 1 <= y&&y <= n2)
        return 1;
    return 0;
}
void dfs(int x, int y, int num)
{
    int i, xxx, yyy;
    xx[num] = x;
    yy[num] = y;
    if (num == n1*n2)
    {
        flag = 1;
        return;
    }
    for (i = 0; i<8; i++)
    {
        xxx = x + dir[i][0];
        yyy = y + dir[i][1];
        if (go(xxx, yyy) && !visit[xxx][yyy] && !flag)
        {
            visit[xxx][yyy] = 1;
            dfs(xxx, yyy, num + 1);
            visit[xxx][yyy] = 0;
        }
    }
}
int main()
{
    int i, k, t;
    scanf("%d", &t);
    for (k = 1; k <= t; k++)
    {
        scanf("%d%d", &n2, &n1);
        memset(visit, 0, sizeof(visit));
        visit[1][1] = 1;
        flag = 0;
        dfs(1, 1, 1);
        printf("Scenario #%d:\n", k);
        if (flag)
        {
            for (i = 1; i <= n1*n2; i++)
                printf("%c%d", xx[i] + ‘A‘ - 1, yy[i]);
        }
        else
            printf("impossible");
        printf(k == t ? "\n" : "\n\n");
    }
    return 0;
}