HDU_3062 Party (2-SAT)

　　2-SAT水题，还wa了好几次，可见本菜更水。。。课件上都有讲解。。。

渣代码：

#include <iostream>
#include <cstring>
#include <cstdio>
#include <stack>

using namespace std;

const int N = 2012;
const int M = 1000000;

struct node {
    int to;
    int next;
} g[M];

int head[N], scc[N];
int dfn[N], low[N];
int t, ind, cnt;
bool vis[N];
stack<int> s;

void init() {
    for(int i = 0; i < N; i++) {
        head[i] = scc[i] = dfn[i] = low[i] = vis[i] = 0;
    }
    t = 1; ind = cnt = 0;
}

void add(int u, int v) {
    g[t].to = v; g[t].next = head[u]; head[u] = t++;
}

void tarjan(int u) {
    int v, i;
    dfn[u] = low[u] = ++ind;
    s.push(u); vis[u] = true;
    for(i = head[u]; i; i = g[i].next) {
        v = g[i].to;
        if(!dfn[v]) {
            tarjan(v);
            low[u] = min(low[u], low[v]);
        } else if(vis[v]) {
            low[u] = min(low[u], dfn[v]);
        }
    }
    if(dfn[u] == low[u]) {
        cnt++;
        do {
            v = s.top(); s.pop();
            scc[v] = cnt;
            vis[v] = false;
        } while(v != u);
    }
}

int main() {
    //freopen("data.in", "r", stdin);

    int n, m, i;
    int a, b, c, d;
    bool flag;
    while(~scanf("%d%d", &n, &m)) {
        init();
        while(m--) {
            scanf("%d%d%d%d", &a, &b, &c, &d);
            if(c == 0) {
                if(d == 0)     {add(a<<1, (b<<1)+1); add(b<<1, (a<<1) + 1);}
                else     {add((a<<1), (b<<1)); add((b<<1)+1, (a<<1)+1);}
            } else {
                if(d == 0)    {add((a<<1) + 1, (b<<1) + 1); add(b<<1, a<<1);}
                else    {add((a<<1)+1, b<<1), add((b<<1)+1, a<<1);}
            }
        }
        for(i = 0; i < n*2; i++) {
            if(!dfn[i])    tarjan(i);
        }
        for(flag = true, i = 0; i < n; i++) {
            if(scc[i*2] == scc[i*2+1]) {
                flag = false;
                cout << "NO" << endl;
                break;
            }
        }
        if(flag)    cout << "YES" << endl;
    }
    return 0;
}