bzoj1823

http://www.lydsy.com/JudgeOnline/problem.php?id=1823

2-sat裸题

#include<bits/stdc++.h>
using namespace std;
const int N = 4010;
struct edge {
    int nxt, to;
} e[N];
int n, m, Time, cot, top, cnt = 1;
int dfn[N], low[N], vis[N], st[N], belong[N], head[N];
void link(int u, int v)
{
    e[++cnt].nxt = head[u];
    head[u] = cnt;
    e[cnt].to = v;
}
void tarjan(int u)
{
    st[++top] = u; dfn[u] = low[u] = ++Time; vis[u] = 1;
    for(int i = head[u]; i; i = e[i].nxt) 
    {
        if(!dfn[e[i].to]) tarjan(e[i].to);
        if(vis[e[i].to]) low[u] = min(low[u], low[e[i].to]);
    }
    if(dfn[u] == low[u]) { ++cot; while(st[top + 1] != u) belong[st[top]] = cot, vis[st[top--]] = 0; } 
}
int main()
{
    int T; scanf("%d", &T);
    while(T--)
    {
        top = 0; cnt = 1;
        memset(e, 0, sizeof(e));
        memset(head, 0, sizeof(head));
        memset(dfn, 0, sizeof(dfn));
        memset(low, 0, sizeof(low));
        memset(belong, 0, sizeof(belong));
        scanf("%d%d", &n, &m);
        for(int i = 1; i <= n; ++i)
        {
            link(i, i + 3 * n);
            link(i + n, i + 2 * n);
        }
        for(int i = 1; i <= n; ++i)
        {
            link(i, i + 3 * n);
            link(i + n, i + 2 * n);
        }
        for(int i = 1; i <= m; ++i)
        {
            char c1[10], c2[10]; int x = 0, y = 0;
            scanf("%s%s", c1, c2);
            for(int i = 1; i < strlen(c1); ++i) x = x * 10 + c1[i] - '0';
            for(int i = 1; i < strlen(c2); ++i) y = y * 10 + c2[i] - '0';        
            if(c1[0] == 'h') x += n; if(c2[0] == 'h') y += n;
            link(x + 2 * n, y); link(y + 2 * n, x);
        }
        bool flag = true;
        for(int i = 1; i <= 4 * n; ++i) if(!dfn[i]) tarjan(i);
        for(int i = 1; i <= 2 * n; ++i) if(belong[i] == belong[i + 2 * n]) 
        { puts("BAD"); flag = false; break; }
        if(flag) puts("GOOD");
    }
    return 0;
}