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;

}