USACO 1.5.4 Checker Challenge
题意:经典的八皇后问题
解法:
采用朴素的每一次放置都与前面的所有行进行比较,在N =13的时候时间会爆掉
《入门经典》上提供的方法很经典,vis数组的使用,具体见《入门经典》125页
/* ID:lsswxr1 PROG:checker LANG:C++ */ #include<iostream> #include<fstream> #include<cmath> #include<cstring> using namespace std; #define maxn 15 ifstream fin("checker.in"); ofstream fout("checker.out"); int N, tot; int outputNums; int curPuts[maxn]; int vis[30][30]; void dfs(int cur) { if (cur == N) { tot++; outputNums++; if (outputNums > 3) { return; } for (int i = 0; i < N; i++) { if (i == 0) { fout << curPuts[i] + 1; } else { fout << " " << curPuts[i] + 1; } } fout << endl; return; } for (int i = 0; i < N; i++) { if (!vis[0][i] && !vis[1][cur + i] && !vis[2][cur - i + N]) { curPuts[cur] = i; vis[0][i] = vis[1][cur + i] = vis[2][cur - i + N] = 1; dfs(cur + 1); vis[0][i] = vis[1][cur + i] = vis[2][cur - i + N] = 0; } } } int main() { fin >> N; tot = 0; memset(vis, 0, sizeof(vis)); memset(curPuts, 0, sizeof(curPuts)); dfs(0); fout << tot << endl; //cout<<ans<<endl; return 0; }