POJ - 2391 最大流

  1 #include <cstdio>
  2 #include <cstring>
  3 #include <algorithm>
  4 #include <vector>
  5 #include <iostream>
  6 #include <queue>
  7 using namespace std;
  8 #define next Next
  9 const int inf = 0x3f3f3f3f;
 10 const int maxn=500;
 11 int level[maxn];
 12 int iter[maxn];
 13 int head[maxn],tot;
 14 struct edge{
 15     int to,cap,Next;
 16 } e[80805]; ///此处应为边的两倍，加一条容量为0的反向边
 17 void init(){
 18     memset(head,-1,sizeof(head));
 19     tot=0;
 20 }
 21 void add(int from,int to,int cap){
 22     e[tot].Next=head[from];
 23     e[tot].to=to;
 24     e[tot].cap=cap;
 25     head[from]=tot;
 26     tot++;
 27 }
 28 void addedge(int from,int to,int cap){
 29     add(from,to,cap);
 30     add(to,from,0);
 31 }
 32 void bfs(int s){
 33     memset(level,-1,sizeof(level));
 34     queue<int> q;
 35     level[s]=0;
 36     q.push(s);
 37     while(!q.empty()){
 38         int v=q.front(); q.pop();
 39         for(int i=head[v];~i;i=e[i].Next){
 40             edge &ed=e[i];
 41             if(ed.cap>0&&level[ed.to]<0){
 42                 level[ed.to]=level[v]+1;
 43                 q.push(ed.to);
 44             }
 45         }
 46     }
 47 }
 48 int dfs(int v,int t,int f){
 49     if(v==t) return f;
 50     for(int &i=iter[v];~i;i=e[i].Next){
 51         edge &ed=e[i];
 52         if(ed.cap>0&&level[v]<level[ed.to]){
 53             int d=dfs(ed.to,t,min(f,ed.cap));
 54             if(d>0){
 55                 ed.cap-=d;
 56                 e[i^1].cap+=d;
 57                 return d;
 58             }
 59         }
 60     }
 61     return 0;
 62 }
 63 int max_flow(int s,int t){
 64     int flow=0;
 65     while(1){
 66         bfs(s);
 67         if(level[t]<0) return flow;
 68         memcpy(iter,head,sizeof(iter));
 69         int f;
 70         while((f=dfs(s,t,inf))>0){
 71             flow+=f;
 72         }
 73     }
 74 }
 75 int niu[maxn],capacity[maxn];
 76 typedef long long ll;
 77 ll dp[maxn][maxn];
 78 void floyd(int n)
 79 {
 80     for(int k=1;k<=n;k++)
 81     {
 82         for(int i=1;i<=n;i++)
 83         {
 84             //if(i==j) continue;
 85             for(int j=1;j<=n;j++)
 86             {
 87                 if(i==k||j==k||i==j) continue;
 88                 dp[i][j] = min(dp[i][j],dp[i][k]+dp[k][j]);
 89             }
 90         }
 91     }
 92 }
 93 int f,p;
 94 void cons(ll T,int s,int t)
 95 {
 96     init();
 97     for(int i=1;i<=f;i++)
 98     {
 99         addedge(s,i,niu[i]);
100         addedge(i,i+f,inf);
101         addedge(i+f,t,capacity[i]);
102     }
103     for(int i=1;i<=f;i++)
104     {
105         for(int j=1;j<=f;j++)
106         {
107             if(i==j) continue;
108             if(dp[i][j]<=T)
109             {
110                 addedge(i,j+f,inf);
111             }
112         }
113     }
114 }
115 int main()
116 {
117     int sum = 0;
118     scanf("%d %d",&f,&p);
119     for(int i=1;i<=f;i++)
120     {
121         scanf("%d %d",&niu[i],&capacity[i]);
122         sum += niu[i];
123     }
124     for(int i=1;i<=f;i++)
125     {
126         for(int j=1;j<=f;j++)
127         {
128             dp[i][j] = 1e15;
129         }
130     }
131     for(int i=1;i<=p;i++)
132     {
133         int x,y;
134         ll w;
135         scanf("%d %d %lld",&x,&y,&w);
136         dp[x][y] = min(dp[x][y],w);   ///一定要注意两点之间的有多条边的情况
137         dp[y][x] = dp[x][y];
138     }
139     floyd(f);
140     ll l = 0,r = 2000000000000LL;
141     ll mid = 0;
142     int s,t;
143     s = 420,t = 421; ///s,t一定要在head数组范围内
144     int flow = 0;
145     ll ans = 0;
146     while(l<=r)
147     {
148         mid = (l+r)/2LL;
149         cons(mid,s,t);
150         flow = max_flow(s,t);
151        // printf("%lld %d\n",mid,flow);
152         if(flow==sum)
153         {
154             ans = mid;
155             r = mid-1;
156         }
157         else
158         {
159             l = mid+1;
160         }
161     }
162     if(ans==0)
163     {
164         puts("-1");
165     }
166     else
167     {
168         printf("%lld\n",ans);
169     }
170     return 0;
171 }
172 /*
173 3 4
174 7 2
175 0 4
176 2 6
177 1 2 40
178 1 2 70
179 1 2 90
180 1 2 120
181 */