USACO1.5.4 checker challenge

以前用pascal 写过的东西，这回是C++。明天去北校区给初中生讲N皇后，所以自己也熟悉一下呗！

/*ID: wangqia6TASK: checkerLANG: C++*/#include <fstream>#include <cstring>using namespace std;const int NEED = 3;ifstream infile;ofstream outfile;int n,now = 0,rec[15];bool leftarr[30],rightarr[30],verarr[30];long ans = 0;void dfsa(int i){if (i > n){now++;for (int j = 1; j < n; j++)outfile << rec[j] << ' ';outfile << rec[n] << endl;return;}for (int j = 1; j <= n; j++)if ( !verarr[j] && !leftarr[i + j] && !rightarr[i - j + n - 1]){verarr[j] = true;leftarr[i + j] = true;rightarr[i - j + n - 1] = true;rec[i] = j;dfsa(i + 1);if (now == NEED)return;verarr[j] = false;leftarr[i + j] = false;rightarr[i - j + n - 1] = false;}return;}void worka(){memset(verarr,0,sizeof(verarr));memset(leftarr,0,sizeof(leftarr));memset(rightarr,0,sizeof(rightarr));dfsa(1); return;}long lowbit(long x){return x & -x;}void dfsb(int i, long verbit,long leftbit,long rightbit){if (i > n){ans++;return;}long k,tmp = verbit & leftbit & rightbit;while (tmp != 0){k = lowbit(tmp);tmp -= k;verbit -= k;leftbit -= k;rightbit -= k;dfsb(i + 1,verbit,(leftbit << 1) + 1,(rightbit >> 1) + (1 << (n-1)));verbit += k;leftbit += k;rightbit += k;}return;}void workb(){ dfsb(1,( 1 << n ) - 1,( 1 << n ) - 1,( 1 << n ) - 1); return;}int main(){infile.open("checker.in");outfile.open("checker.out");infile >> n;worka();workb();outfile << ans << endl;infile.close();outfile.close();return 0;}