POJ 1966 Cable TV Network

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <cmath>
  5 #include <algorithm>
  6 #include <climits>
  7 #include <vector>
  8 #include <queue>
  9 #include <cstdlib>
 10 #include <string>
 11 #include <set>
 12 #include <stack>
 13 #define LL long long
 14 #define pii pair<int,int>
 15 #define INF 0x3f3f3f3f
 16 using namespace std;
 17 const int maxn = 200;
 18 struct arc{
 19     int to,flow,next;
 20     arc(int x = 0,int y = 0,int z = -1){
 21         to = x;
 22         flow = y;
 23         next = z;
 24     }
 25 };
 26 arc e[maxn*maxn];
 27 int head[maxn],d[maxn],cur[maxn];
 28 int S,T,n,m,tot,cnt;
 29 pii rec[maxn*maxn];
 30 void add(int u,int v,int flow){
 31     e[tot] = arc(v,flow,head[u]);
 32     head[u] = tot++;
 33     e[tot] = arc(u,0,head[v]);
 34     head[v] = tot++;
 35 }
 36 bool bfs(){
 37     memset(d,-1,sizeof(d));
 38     d[S] = 1;
 39     queue<int>q;
 40     q.push(S);
 41     while(!q.empty()){
 42         int u = q.front();
 43         q.pop();
 44         for(int i = head[u]; ~i; i = e[i].next){
 45             if(e[i].flow > 0 && d[e[i].to] == -1){
 46                 d[e[i].to] = d[u] + 1;
 47                 q.push(e[i].to);
 48             }
 49         }
 50     }
 51     return d[T] > -1;
 52 }
 53 int dfs(int u,int low){
 54     if(u == T) return low;
 55     int tmp = 0,a;
 56     for(int &i = cur[u]; ~i; i = e[i].next){
 57         if(e[i].flow > 0&& d[e[i].to] == d[u] + 1&&(a=dfs(e[i].to,min(e[i].flow,low)))){
 58             e[i].flow -= a;
 59             e[i^1].flow += a;
 60             rec[cnt++] = make_pair(i,a);
 61             rec[cnt++] = make_pair(i^1,-a);
 62             low -= a;
 63             tmp += a;
 64             if(!low) break;
 65         }
 66     }
 67     if(!tmp) d[u] = -1;
 68     return tmp;
 69 }
 70 int dinic(){
 71     int ans = cnt = 0;
 72     while(bfs()){
 73         memcpy(cur,head,sizeof(head));
 74         ans += dfs(S,INF);
 75     }
 76     return ans;
 77 }
 78 void release(){
 79     for(int i = 0; i < cnt; ++i)
 80         e[rec[i].first].flow += rec[i].second;
 81 }
 82 int main(){
 83     int u,v;
 84     while(~scanf("%d %d",&n,&m)){
 85         memset(head,-1,sizeof(head));
 86         if(!m){
 87             if(n == 1) puts("1");
 88             else puts("0");
 89             continue;
 90         }
 91         for(int i = tot = 0; i < m; ++i){
 92             scanf(" (%d,%d)",&u,&v);
 93             add(u+n,v,INF);
 94             add(v+n,u,INF);
 95         }
 96         for(int i = 0; i < n; ++i)
 97             add(i,i+n,1);
 98         S = n;
 99         int ans = INF;
100         for(int i = 1; i < n; ++i){
101             T = i;
102             ans = min(ans,dinic());
103             release();
104         }
105         printf("%d\n",ans == INF?n:ans);
106     }
107     return 0;
108 }