usaco Checker Challenge

很朴实的DFS没有加任何剪枝和优化，0.7sec ~~

code：

/*ID: yueqiqLANG: C++TASK: checker*/#include <set>#include <map>#include <ctime>#include <queue>#include <cmath>#include <stack>#include <limits>#include <vector>#include <bitset>#include <string>#include <cstdio>#include <cstring>#include <fstream>#include <string.h>#include <iostream>#include <algorithm>#define ls rt<<1#define rs rt<<1|1#define Si set<int>#define LL long long#define pb push_back#define PS printf(" ")#define Vi vector<int>#define LN printf("\n")#define SD(a) scanf("%d",&a)#define PD(a) printf("%d",a)#define SET(a,b) memset(a,b,sizeof(a))#define FF(i,a) for(int i(0);i<(a);i++)#define FD(i,a) for(int i(a);i>=(1);i--)#define FOR(i,a,b) for(int i(a);i<=(b);i++)#define FOD(i,a,b) for(int i(a);i>=(b);i--)#define readf freopen("checker.in","r",stdin)#define writef freopen("checker.out","w",stdout)const double pi = acos(-1.0);const int maxn = 50;const int BigP = 99999999;const int INF = 99999999;const int dx[]={0,1,0,-1};const int dy[]={1,0,-1,0};using namespace std;int N,ans;bool visx[maxn],visy[maxn],vis1[maxn],vis2[maxn];//vis1 2-2N vis2 1-(2N-1);//p is 列int path[21];int count=0;bool can(int x,int y){    if(visx[x]) return false;    if(visy[y]) return false;    if(vis1[x+y]) return false;    if(vis2[N-y+x]) return false;    return true;}void dfs(int p){    if(p>N){        ans++;        if(ans<=3){            FOR(i,1,N-1) printf("%d ",path[i]);            printf("%d\n",path[N]);        }        return ;    }    FOR(i,1,N){        if(can(i,p)){            visx[i]=true;            visy[p]=true;            vis1[i+p]=true;            vis2[N-p+i]=true;            path[p]=i;            dfs(p+1);            visx[i]=false;            visy[p]=false;            vis1[i+p]=false;            vis2[N-p+i]=false;        }    }}int main(){    readf;    writef;    SD(N);    dfs(1);    PD(ans);LN;    return 0;}