Poj 2135 Farm Tour

  1 #include <iostream>
  2 #include <cstring>
  3 #include <cstdio>
  4 #include <cstdlib>
  5 #include <cmath>
  6 #include <string>
  7 #include <vector>
  8 #include <list>
  9 #include <map>
 10 #include <queue>
 11 #include <stack>
 12 #include <bitset>
 13 #include <algorithm>
 14 #include <numeric>
 15 #include <functional>
 16 #include <set>
 17 #include <fstream>
 18 
 19 using namespace std;
 20 
 21 const int maxn=10010;
 22 const int INF=0x7fffffff;
 23 int N,M;
 24 int a[maxn],b[maxn],c[maxn];
 25 struct edge {
 26     int to,cap,cost,rev;
 27 };
 28 int V;
 29 vector<edge> G[maxn];
 30 int dist[maxn];
 31 int prevv[maxn],preve[maxn];
 32 /*
 33 void add_edge(int from,int to,int cap,int cost)
 34 {
 35     G[from].push_back((edge){to,cap,cost,(int)G[to].size()});
 36     G[to].push_back((edge){from,0,-cost,(int)G[from].size()-1});
 37 }
 38 
 39 int min_cost_flow(int s,int t,int f)
 40 {
 41     int res=0;
 42     while (f>0) {
 43         fill(dist, dist+V, INF);
 44         dist[s]=0;
 45         bool update=true;
 46         while (update) {
 47             update=false;
 48             for (int v=0; v<V; v++) {
 49                 if (dist[v]==INF) {
 50                     continue;
 51                 }
 52                 for (int i=0; i<G[v].size(); i++) {
 53                     edge &e=G[v][i];
 54                     if (e.cap>0&&dist[e.to]>dist[v]+e.cost) {
 55                         dist[e.to]=dist[v]+e.cost;
 56                         prevv[e.to]=v;
 57                         preve[e.to]=i;
 58                         update=true;
 59                     }
 60                 }
 61             }
 62         }
 63         if (dist[t]==INF) {
 64             return -1;
 65         }
 66         int d=f;
 67         for (int v=t; v!=s; v=prevv[v]) {
 68             d=min(d,G[prevv[v]][preve[v]].cap);
 69         }
 70         f-=d;
 71         res+=d*dist[t];
 72         for (int v=t; v!=s; v=prevv[v]) {
 73             edge &e=G[prevv[v]][preve[v]];
 74             e.cap-=d;
 75             G[v][e.rev].cap+=d;
 76         }
 77     }
 78     return res;
 79 }
 80 */
 81 int h[maxn];
 82 typedef pair<int, int> P;
 83 void add_edge(int from,int to,int cap,int cost)
 84 {
 85     G[from].push_back((edge){to,cap,cost,(int)G[to].size()});
 86     G[to].push_back((edge){from,0,-cost,(int)G[from].size()-1});
 87 }
 88 
 89 int min_cost_flow(int s,int t,int f)
 90 {
 91     int res=0;
 92     fill(h, h+V, 0);
 93     while (f>0) {
 94         priority_queue<P,vector<P>,greater<P> > que;
 95         fill(dist, dist+V, INF);
 96         dist[s]=0;
 97         que.push(P(0,s));
 98         while (!que.empty()) {
 99             P p=que.top();
100             que.pop();
101             int v=p.second;
102             if (dist[v]<p.first) {
103                 continue;
104             }
105             for (int i=0; i<G[v].size(); i++) {
106                 edge &e=G[v][i];
107                 if (e.cap>0&&dist[e.to]>dist[v]+e.cost+h[v]-h[e.to]) {
108                     dist[e.to]=dist[v]+e.cost+h[v]-h[e.to];
109                     prevv[e.to]=v;
110                     preve[e.to]=i;
111                     que.push(P(dist[e.to],e.to));
112                 }
113             }
114         }
115         if (dist[t]==INF) {
116             return -1;
117         }
118         for (int v=0; v<V; v++) {
119             h[v]+=dist[v];
120         }
121         int d=f;
122         for (int v=t; v!=s; v=prevv[v]) {
123             d=min(d,G[prevv[v]][preve[v]].cap);
124         }
125         f-=d;
126         res+=d*h[t];
127         for (int v=t; v!=s; v=prevv[v]) {
128             edge &e=G[prevv[v]][preve[v]];
129             e.cap-=d;
130             G[v][e.rev].cap+=d;
131         }
132     }
133     return res;
134 }
135 
136 int main()
137 {
138     //freopen("/Users/apple/Desktop/2135/2135/in", "r", stdin);
139     //freopen("/Users/apple/Desktop/2135/2135/out", "w", stdout);
140     while ((scanf("%d%d",&N,&M))!=EOF) {
141         V=N;
142         for (int i=0; i<M; i++) {
143             scanf("%d%d%d",&a[i],&b[i],&c[i]);
144         }
145         int s=0,t=N-1;
146         for (int i=0; i<M; i++) {
147             add_edge(a[i]-1, b[i]-1, 1, c[i]);
148             add_edge(b[i]-1, a[i]-1, 1, c[i]);
149         }
150         int res2=min_cost_flow(s, t, 2);
151         printf("%d\n",res2);
152     }
153     return 0;
154 }