86 lines
1.8 KiB
C++
86 lines
1.8 KiB
C++
#include<cstdio>
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#include<cstring>
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#include<algorithm>
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#include<vector>
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using namespace std;
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const int maxn=2000+50;
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int n,m;
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int a[maxn],b[maxn];
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int c[maxn],d[maxn];
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struct TwoSAT
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{
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int n;
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vector<int> G[maxn*2];
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int S[maxn*2],c;
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bool mark[maxn*2];
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bool dfs(int x)
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{
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if(mark[x^1]) return false;
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if(mark[x]) return true;
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mark[x]=true;
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S[c++]=x;
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for(int i=0;i<G[x].size();i++)
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if(!dfs(G[x][i])) return false;
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return true;
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}
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void init(int n)
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{
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this->n=n;
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for(int i=0;i<2*n;i++) G[i].clear();
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memset(mark,0,sizeof(mark));
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}
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void add_clause(int x,int xval,int y,int yval)
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{
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x=x*2+xval;
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y=y*2+yval;
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G[x].push_back(y);
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}
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bool solve()
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{
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for(int i=0;i<2*n;i+=2)
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if(!mark[i] && !mark[i+1])
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{
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c=0;
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if(!dfs(i))
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{
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while(c>0) mark[S[--c]]=false;
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if(!dfs(i+1)) return false;
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}
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}
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return true;
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}
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}TS;
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bool ok(int mid)
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{
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TS.init(n);
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for(int i=0;i<n/2;i++)
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{
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TS.add_clause(a[i],0,b[i],1);
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TS.add_clause(b[i],0,a[i],1);
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}
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for(int i=0;i<mid;i++)
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{
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TS.add_clause(c[i],1,d[i],0);
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TS.add_clause(d[i],1,c[i],0);
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}
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return TS.solve();
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}
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int main()
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{
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while(scanf("%d%d",&n,&m)==2&&n)
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{
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n*=2;
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for(int i=0;i<n/2;i++) scanf("%d%d",&a[i],&b[i]);
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for(int i=0;i<m;i++) scanf("%d%d",&c[i],&d[i]);
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int L=0, R=m;
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while(R>L)
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{
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int mid = L+(R-L+1)/2;
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if(ok(mid)) L=mid;
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else R=mid-1;
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}
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printf("%d\n",L);
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}
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return 0;
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}
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