820 - Internet bandwidth/820.cpp

   1 /*
   2   Accepted
   3  */
   4 #include <iostream>
   5 #include <iterator>
   6 #include <queue>
   7 #include <stdio.h>
   8
   9 using namespace std;
  10
  11 const int MAXN = 101;
  12
  13 int cap[MAXN+1][MAXN+1], flow[MAXN+1][MAXN+1], prev[MAXN+1];
  14
  15 int fordFulkerson(int n, int s, int t){
  16   int ans = 0;
  17   for (int i=0; i<n; ++i) fill(flow[i], flow[i]+n, 0);
  18   while (true){
  19     fill(prev, prev+n, -1);
  20     queue<int> q;
  21     q.push(s);
  22     while (q.size() && prev[t] == -1){
  23       int u = q.front();
  24       q.pop();
  25       for (int v = 0; v<n; ++v)
  26         if (v != s && prev[v] == -1 && cap[u][v] > 0 && cap[u][v] - flow[u][v] > 0)
  27           prev[v] = u, q.push(v);
  28     }
  29
  30     if (prev[t] == -1) break;
  31
  32     int bottleneck = INT_MAX;
  33     for (int v = t, u = prev[v]; u != -1; v = u, u = prev[v]){
  34       bottleneck = min(bottleneck, cap[u][v] - flow[u][v]);
  35     }
  36     for (int v = t, u = prev[v]; u != -1; v = u, u = prev[v]){
  37       flow[u][v] += bottleneck;
  38       flow[v][u] = -flow[u][v];
  39     }
  40     ans += bottleneck;
  41   }
  42   return ans;
  43 }
  44
  45 int main(){
  46   int n, runs = 1;
  47   while (scanf("%d", &n) == 1 && n){
  48     for (int i=0; i<n; ++i){
  49       fill(cap[i], cap[i]+n, 0);
  50     }
  51     int s, t, C;
  52     scanf("%d %d %d", &s, &t, &C);
  53     --s, --t;
  54     while (C--){
  55       int i, j, k;
  56       scanf("%d %d %d", &i, &j, &k);
  57       cap[--i][--j] += k, cap[j][i] += k;
  58     }
  59
  60     printf("Network %d\nThe bandwidth is %d.\n\n", runs++, fordFulkerson(n, s, t));
  61   }
  62   return 0;
  63 }