洛谷 P1379 八数码难题

#include <cstdio>
int goal[4][4]={{0,0,0,0},
                {0,1,2,3},
                {0,8,0,4},
                {0,7,6,5}};
int fx[5] = {0,-1,1,0},fy[5] = {-1,0,0,1},ans,now[4][4];
bool flag = false;
char str[10];
void swap (int & m,int & n)
{
    int tmp = m;
    m = n;
    n = tmp;
}
bool judge()
{
    for (int i = 1; i <= 3; ++i)
     for (int j = 1; j <= 3; ++j)
      if (now[i][j] != goal[i][j]) return false;
    return true;
}
void dfs(int step,int x,int y,int pre)
{
    if (flag) return;
    if (step > ans) return;
    if (step == ans)
    {
        if(judge()) flag=true;
        return;
    }
    for (int i = 0; i < 4; ++i)
    {
        if(i+pre==3) continue;
        int tx = x + fx[i],ty = y + fy[i];
        if(tx >= 1 && tx <= 3 && ty >= 1 && ty <= 3)
        {
            swap (now[x][y],now[tx][ty]);
            dfs(step+1, tx, ty,i);
            swap (now[x][y],now[tx][ty]);
        }
    }
}
int main()
{
    scanf("%s",str);
    now[1][1] = str[0] - ‘0‘; now[1][2] = str[1] - ‘0‘; now[1][3] = str[2] - ‘0‘;
    now[2][1] = str[3] - ‘0‘; now[2][2] = str[4] - ‘0‘; now[2][3] = str[5] - ‘0‘;
    now[3][1] = str[6] - ‘0‘; now[3][2] = str[7] - ‘0‘; now[3][3] = str[8] - ‘0‘;
    int x, y;
    for (int i = 1; i <= 3; ++i)
     for (int j = 1; j <= 3; ++j)
      if (!now[i][j]) x = i, y = j;
    for (ans = 1;;++ans)
    {
        dfs(0, x, y, 1107);
        if (flag) break;
    }
    printf("%d\n",ans);
    return 0;
}