Hdu1814 peaceful Commission, 2-Sat

Question:One country has n parties, each of which has two representatives in the Parliament. Now we want to form a Peace Committee. We want to select one from the representatives of each party in the Parliament, A total of n members form the Peace Committee. It is known that there is hatred between some representatives. That is to say, they cannot be elected as members of the Peace Commission at the same time. Do you want to determine whether a peace commission meeting the requirements can be created? If yes, please provide any solution.

2-SAT problems

#include <cstdio>#include <cstring>#include <vector>#include <iostream>#include <algorithm>using namespace std;const int maxn = 10005;int n, m;vector<int> G[maxn*2];bool mark[maxn*2];int S[maxn*2], top;bool dfs(int x){    if(mark[x^1]) return false;    if(mark[x]) return true;    mark[x] = true;    S[top++] = x;    for(int i=0; i<G[x].size(); ++i)        if(!dfs(G[x][i])) return false;    return true;}bool TwoSat(){    memset(mark, 0, sizeof mark );    for(int i=0; i<n; i += 2) {        if(!mark[i] && !mark[i^1]) {            top = 0;            if(!dfs(i)) {                while(top) mark[S[--top]] = false;                if(!dfs(i^1)) return false;            }        }    }    return true;}int main(){    int u, v;    while(~scanf("%d%d", &n, &m)) {        n *= 2;        for(int i=0; i<n; ++i) G[i].clear();        while(m--) {            scanf("%d%d", &u, &v);            u--;            v--;            G[u].push_back(v^1);            G[v].push_back(u^1);        }        if(TwoSat()) {            for(int i=0; i<n; i+=2)                if(mark[i])                    printf("%d\n", i+1);                else                    printf("%d\n", (i^1)+1);        } else printf("NIE\n");    }    return 0;}

Hdu1814 peaceful Commission, 2-Sat