bzoj 2095 Poi2010 Bridges 混合图欧拉回路

  1 #include<iostream>
  2 #include<cstdio>
  3 #include<cstring>
  4 #include<algorithm>
  5 #include<queue>
  6 #define inf 0x3f3f3f3f
  7 #define N 2005
  8 #define M 100005
  9 using namespace std;
 10 int head[N],ver[M],f[M],nxt[M],tot;
 11 void add(int a,int b,int c)
 12 {
 13     c=abs(c);
 14     tot++;nxt[tot]=head[a];head[a]=tot;ver[tot]=b;f[tot]=c;
 15     tot++;nxt[tot]=head[b];head[b]=tot;ver[tot]=a;f[tot]=0;
 16     return ;
 17 }
 18 int ch[N],S,T;
 19 queue<int>q;
 20 bool tell()
 21 {
 22     memset(ch,-1,sizeof(ch));
 23     q.push(S);ch[S]=0;
 24     while(!q.empty())
 25     {
 26         int tmp=q.front();q.pop();
 27         for(int i=head[tmp];i;i=nxt[i])
 28         {
 29             if(ch[ver[i]]==-1&&f[i])
 30             {
 31                 ch[ver[i]]=ch[tmp]+1;
 32                 q.push(ver[i]);
 33             }
 34         }
 35     }
 36     return ch[T]!=-1;
 37 }
 38 int zeng(int a,int b)
 39 {
 40     if(a==T)return b;
 41     int r=0;
 42     for(int i=head[a];i&&b>r;i=nxt[i])
 43     {
 44         if(f[i]&&ch[ver[i]]==ch[a]+1)
 45         {
 46             int t=zeng(ver[i],min(f[i],b-r));
 47             f[i]-=t;f[i^1]+=t;r+=t;
 48         }
 49     }
 50     if(!r)ch[a]=-1;
 51     return r;
 52 }
 53 int dinic()
 54 {
 55     int r=0,t;
 56     while(tell())while(t=zeng(S,inf))r+=t;
 57     return r;
 58 }
 59 int bian[2005][4];
 60 int n,m;
 61 int fa[2005];
 62 int find(int x)
 63 {
 64     if(x==fa[x])return x;
 65     return fa[x]=find(fa[x]);
 66 }
 67 int du[N];
 68 bool pan(int x)
 69 {
 70     tot=1;
 71     memset(head,0,sizeof(head));
 72     memset(du,0,sizeof(du));
 73     S=0;T=n+1;
 74     for(int i=1;i<=n;i++)fa[i]=i;
 75     for(int i=1;i<=m;i++)
 76     {
 77         int xx=bian[i][0],yy=bian[i][1];
 78         if(bian[i][3]<=x||bian[i][2]<=x)
 79         {
 80             if(bian[i][2]<=x)
 81             {
 82                 du[xx]++;du[yy]--;
 83                 if(bian[i][3]<=x)
 84                 {
 85                     add(yy,xx,1);
 86                 }
 87             }
 88             else 
 89             {
 90                 du[xx]--;du[yy]++;
 91             }
 92             int aa=find(xx),bb=find(yy);
 93             if(aa!=bb)fa[aa]=bb;
 94         }
 95     }
 96     for(int i=2;i<=n;i++)if(find(i)!=find(i-1))return 0;
 97     int now=0;
 98     for(int i=1;i<=n;i++)
 99     {
100         if(du[i]%2!=0)return 0;
101         if(du[i]<0)
102         {
103             add(S,i,du[i]/2);
104             now-=du[i]/2;
105         }
106         else add(i,T,du[i]/2);
107     }
108     return dinic()==now;
109 }
110 int main()
111 {
112     scanf("%d%d",&n,&m);
113     int mn=inf,mx=0;
114     for(int i=1;i<=n;i++)fa[i]=i;
115     for(int i=1;i<=m;i++)
116     {
117         scanf("%d%d%d%d",&bian[i][0],&bian[i][1],&bian[i][2],&bian[i][3]);
118         mn=min(mn,bian[i][2]);mx=max(mx,bian[i][2]);
119         mn=min(mn,bian[i][3]);mx=max(mx,bian[i][3]);
120     }
121     int l=mn,r=mx;
122     while(l<=r)
123     {
124         int mid=(l+r)>>1;
125         if(pan(mid))r=mid-1;
126         else l=mid+1;
127     }
128     if(l==mx+1)puts("NIE");
129     else printf("%d\n",l);
130     return 0;
131 }