BZOJ1532: [POI2005]Kos-Dicing

  1 #include<cstdio>
  2 
  3 #include<cstdlib>
  4 
  5 #include<cmath>
  6 
  7 #include<cstring>
  8 
  9 #include<algorithm>
 10 
 11 #include<iostream>
 12 
 13 #include<vector>
 14 
 15 #include<map>
 16 
 17 #include<set>
 18 
 19 #include<queue>
 20 
 21 #include<string>
 22 
 23 #define inf 1000000000
 24 
 25 #define maxn 150000
 26 
 27 #define maxm 150000
 28 
 29 #define eps 1e-10
 30 
 31 #define ll long long
 32 
 33 #define pa pair<int,int>
 34 
 35 #define for0(i,n) for(int i=0;i<=(n);i++)
 36 
 37 #define for1(i,n) for(int i=1;i<=(n);i++)
 38 
 39 #define for2(i,x,y) for(int i=(x);i<=(y);i++)
 40 
 41 #define for3(i,x,y) for(int i=(x);i>=(y);i--)
 42 
 43 using namespace std;
 44 
 45 inline int read()
 46 
 47 {
 48 
 49     int x=0,f=1;char ch=getchar();
 50 
 51     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
 52 
 53     while(ch>=‘0‘&&ch<=‘9‘){x=10*x+ch-‘0‘;ch=getchar();}
 54 
 55     return x*f;
 56 
 57 }
 58 int  n,m,s,t,maxflow,tot=1,a[maxn],b[maxn],head[maxn],cur[maxn],h[maxn],q[maxn];
 59 
 60 struct edge{int go,next,v;}e[maxm];
 61 
 62 void ins(int x,int y,int z){e[++tot].go=y;e[tot].v=z;e[tot].next=head[x];head[x]=tot;}
 63 
 64 void insert(int x,int y,int z){ins(x,y,z);ins(y,x,0);}
 65 
 66 bool bfs()
 67 
 68 {
 69 
 70     for(int i=s;i<=t;i++)h[i]=-1;
 71 
 72     int l=0,r=1;q[1]=s;h[s]=0;
 73 
 74     while(l<r)
 75 
 76     {
 77 
 78         int x=q[++l];
 79 
 80         for(int i=head[x];i;i=e[i].next)
 81 
 82          if(e[i].v&&h[e[i].go]==-1)
 83 
 84          {
 85 
 86             h[e[i].go]=h[x]+1;q[++r]=e[i].go;
 87 
 88          }
 89 
 90     }
 91 
 92     return h[t]!=-1;
 93 
 94 }
 95 
 96 int dfs(int x,int f)
 97 
 98 {
 99 
100     if(x==t) return f;
101 
102     int tmp,used=0;
103 
104     for(int i=head[x];i;i=e[i].next)
105 
106      if(e[i].v&&h[e[i].go]==h[x]+1)
107 
108     {
109 
110         tmp=dfs(e[i].go,min(e[i].v,f-used));
111 
112         e[i].v-=tmp;if(e[i].v)cur[x]=i;
113 
114         e[i^1].v+=tmp;used+=tmp;
115 
116         if(used==f)return f;       
117 
118     }
119 
120     if(!used) h[x]=-1;
121 
122     return used;
123 
124 }
125 
126 void dinic()
127 
128 {
129 
130     maxflow=0;
131 
132     while(bfs())
133 
134     {
135 
136         for (int i=s;i<=t;i++)cur[i]=head[i];maxflow+=dfs(s,inf);
137 
138     }
139 
140 }
141 inline bool check(int x)
142 {
143     memset(head,0,sizeof(head));tot=1;s=0;t=n+m+1;
144     for1(i,m)
145      {
146         insert(s,i,1);
147         insert(i,m+a[i],1);insert(i,m+b[i],1);
148      }
149     for1(i,n)insert(m+i,t,x);
150     dinic();
151     return maxflow==m;
152 } 
153 
154 int main()
155 
156 {
157 
158     freopen("input.txt","r",stdin);
159 
160     freopen("output.txt","w",stdout);
161 
162     n=read();m=read();
163     for1(i,m)a[i]=read(),b[i]=read();
164     int l=1,r=m,mid;
165     while(l<=r)
166     {
167          mid=(l+r)>>1;
168         if(check(mid))r=mid-1;else l=mid+1;
169     }
170     printf("%d\n",l);     
171 
172     return 0;
173 
174 }