P4171 [JSOI2010]滿漢全席（2-sat）

模型：兩個至少選一個。

#include<bits/stdc++.h>
#define ll long long
#define MP make_pair
#define P pair<long long, long long>
using namespace std;
const int N = 2e3 + 10;
int t, n, m, h[N], cnt;
int dfn[N], scc[N], ins[N], low[N], ind, col;
stack<int> s;
char l[3], r[3];
struct node {
    int v, nt;
} no[N];
void add(int u, int v) {
    no[cnt] = node{v, h[u]};
    h[u] = cnt++;
}
void tarjan(int u) {
    dfn[u] = low[u] = ++ind;
    ins[u] = 1;
    s.push(u);
    for(int i = h[u]; ~i; i = no[i].nt) {
        int v = no[i].v;
        if(!dfn[v])
            tarjan(v), low[u] = min(low[u], low[v]);
        else if(ins[v])
            low[u] = min(low[u], dfn[v]);
    }
    if(low[u] == dfn[u]) {
        ++col;
        int v;
        do {
            v = s.top();
            s.pop();
            scc[v] = col;
            ins[v] = 0;
        } while(u != v);
    }
}
int check() {
    for(int i = 1; i <= n; i++)
        if(scc[i] == scc[i + n])
            return 0;
    return 1;
}
int main() {
    scanf("%d", &t);
    while(t--) {
        while(!s.empty())
            s.pop();
        scanf("%d%d", &n, &m);
        memset(h, -1, sizeof h), cnt = ind = col = 0;
        memset(dfn, 0, sizeof dfn);
        memset(ins, 0, sizeof ins);
        for(int x, y, i = 1; i <= m; i++) {
            scanf("%1s%d %1s%d", l, &x, r, &y);
            if(l[0] == 'm' && r[0] == 'm')
                add(x + n, y), add(y + n, x);
            if(l[0] == 'h' && r[0] == 'h')
                add(x, y + n), add(y, x + n);
            if(l[0] == 'h' && r[0] == 'm')
                add(x, y), add(y + n, x + n);
            if(l[0] == 'm' && r[0] == 'h')
                add(x + n, y + n), add(y, x);
        }
        for(int i = 1; i <= n * 2; i++)
            if(!dfn[i])
                tarjan(i);
        printf(check() ? "GOOD\n" : "BAD\n");
    }
    return 0;
}