uva 12745 Wishmaster(2-sat)

12745 Wishmaster

view code#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;
typedef long long ll;
const int N = 200010;
const int M = N<<1;
int _, cas=1, n, m, pre[N], S[N], c;
bool mark[N];

struct edge
{
    int u, v, next;
    edge() {}
    edge(int u, int v, int next):u(u),v(v),next(next) {}
}e[M];
int ecnt = 0;

void addedge(int u, int v)
{
    if(u<0) u = -u+n;
    if(v<0) v = -v+n;
    e[ecnt] = edge(u, v, pre[u]);
    pre[u] = ecnt++;
}

bool dfs(int x)
{
    int ano = x>n?x-n:x+n;
    if(mark[ano]) return false;
    if(mark[x]) return true;
    mark[x] = true;
    S[c++] = x;
    for(int i=pre[x]; ~i; i=e[i].next)
    {
        int v = e[i].v;
        if(!dfs(v)) return false;
    }
    return 1;
}

bool check()
{
    for(int i=1; i<=n; i++)
    {
        if(!mark[i] && !mark[i+n])
        {
            c = 0;
            if(!dfs(i)){
                while(c>0) mark[S[--c]] = 0;
                if(!dfs(i+n)) return 0;
            }
        }
    }
    return 1;
}

void solve()
{
    scanf("%d%d", &n, &m);
    int u, v;
    ecnt = 0;
    memset(pre, -1, sizeof(pre));
    for(int i=0; i<m; i++)
    {
        scanf("%d%d", &u, &v);
        addedge(-u, v);
        addedge(-v, u);
    }

    memset(mark, 0, sizeof(mark));
    printf("Case %d: ", cas++);
    if(check()) puts("Yes");
    else puts("No");
}

int main()
{
//    freopen("in.txt", "r", stdin);
    cin>>_;
    while(_--) solve();
    return 0;
}