https://ac.nowcoder.com/acm/contest/327/F

C++版本一

std

题解: 2-sat 图论

#include <bits/stdc++.h>
using namespace std;
#define ll long long
 
const int MAXN = 400010;
const int MAXM = 800010;
struct Edge
{
    int to,next;
}edge[MAXM];
int head[MAXN],tot;
void init()
{
    tot = 0;
    memset(head,-1,sizeof(head));
}
void addedge(int u,int v)
{
    edge[tot].to = v; edge[tot].next = head[u]; head[u] = tot++;
}
int Low[MAXN],DFN[MAXN],Stack[MAXN],Belong[MAXN];
int Index,top;
int scc;
bool Instack[MAXN];
int num[MAXN];
 
void Tarjan(int u)
{
    int v;
    Low[u] = DFN[u] = ++Index;
    Stack[top++] = u;
    Instack[u] = true;
    for(int i = head[u];i != -1;i = edge[i].next)
    {
        v = edge[i].to;
        if( !DFN[v] )
        {
            Tarjan(v);
            if(Low[u] > Low[v])Low[u] = Low[v];
        }
        else if(Instack[v] && Low[u] > DFN[v])
        Low[u] = DFN[v];
    }
    if(Low[u] == DFN[u])
    {
        scc++;
        do
        {
            v = Stack[--top];
            Instack[v] = false;
            Belong[v] = scc;
            num[scc]++;
        }
        while(v != u);
    }
}
 
bool solvable(int n)
{
    memset(DFN,0,sizeof(DFN));
    memset(Instack,false,sizeof(Instack));
    memset(num,0,sizeof(num));
    Index = scc = top = 0;
    for(int i = 0;i < n;i++)
    if(!DFN[i])
    Tarjan(i);
    for(int i = 0;i < n;i += 2)
    {
        if(Belong[i] == Belong[i^1])
        return false;
    }
    return true;
}
 
int n,m;
int a[200005];
vector<int> v[200005];
 
int main()
{
    scanf("%d%d",&n,&m);
    init();
    for (int i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
    }
    for (int i=0;i<m;i++)
    {
        int k;
        scanf("%d",&k);
        for (int j=1;j<=k;j++)
        {
            int x;
            scanf("%d",&x);
            v[x].push_back(i);
        }
    }
    for (int i=1;i<=n;i++)
    {
        if (v[i].size()==2)
        {
            if (a[i]==1)
            {
                int x=v[i][0]<<1;
                int y=v[i][1]<<1;
                addedge(x,y^1);
                addedge(x^1,y);
                addedge(y,x^1);
                addedge(y^1,x);
            }
            else
            {
                int x=v[i][0]<<1;
                int y=v[i][1]<<1;
                addedge(x,y);
                addedge(x^1,y^1);
                addedge(y,x);
                addedge(y^1,x^1);
            }
        }
        else if (v[i].size()==1)
        {
            if (a[i]==1)
            {
                int x=v[i][0]<<1;
                addedge(x,x^1);
            }
            else
            {
                int x=v[i][0]<<1;
                addedge(x^1,x);
            }
        }
        else if (v[i].size()==0)
        {
            if (a[i]==1)
            {
                addedge(0,0);
                addedge(1,1);
            }
        }
    }
    if (solvable(m<<1)) puts("YES");
    else puts("NO");
    return 0;
}