poj 3678 Katu Puzzle(Two Sat)
题目链接:http://poj.org/problem?id=3678
代码:
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#include<cstdio> #include<cstring> #include<iostream> #include<algorithm> #include<vector> using namespace std; const int maxn = 1050; struct Two_Sat { int n; vector<int> G[maxn*2]; bool mark[maxn*2]; int s[maxn*2],cnt; void init(int n) { this->n = n; memset(mark,0,sizeof(mark)); for(int i=0; i<n*2; i++) G[i].clear(); } void add_clause(int u,int v,int flag,char symbol) { u = u*2 + flag; v = v*2 + flag; if(symbol == 'A') { if(flag) { G[u].push_back(v); G[v].push_back(u); G[u^1].push_back(u); G[v^1].push_back(v); } else { G[u^1].push_back(v); G[v^1].push_back(u); } } else if(symbol == 'O') { if(flag) { G[u^1].push_back(v); G[v^1].push_back(u); } else { G[u].push_back(v); G[v].push_back(u); G[u^1].push_back(u); G[v^1].push_back(v); } } else { if(flag) { G[u^1].push_back(v); G[v].push_back(u^1); G[v^1].push_back(u); G[u].push_back(v^1); } else { G[u].push_back(v); G[v].push_back(u); G[u^1].push_back(v^1); G[v^1].push_back(u^1); } } } bool dfs(int u) { if(mark[u^1]) return false; if(mark[u]) return true; mark[u] = true; s[cnt++] = u; for(int i=0; i<G[u].size(); i++) { if(!dfs(G[u][i])) return false; } return true; } bool solve() { for(int i=0; i<n*2; i+=2) { if(!mark[i] && !mark[i+1]) { cnt = 0; if(!dfs(i)) { while(cnt>0) mark[s[--cnt]] = false; if(!dfs(i+1)) return false; } } } return true; } }solver; int main() { //freopen("E:\\acm\\input.txt","r",stdin); int N,M; while(cin>>N>>M) { solver.init(N); for(int i=1; i<=M; i++) { int a,b,c; char s[5]; scanf("%d %d %d %s",&a,&b,&c,s); solver.add_clause(a,b,c,s[0]); } if(solver.solve()) printf("YES\n"); else printf("NO\n"); } }