ACM: 网络流 图论 poj 1459

 

                                                                Power Network

Description

A power network consists of nodes (power stations, consumers and dispatchers) connected by power transport lines. A node u may be supplied with an amount s(u) >= 0 of power, may produce an amount 0 <= p(u) <= p_max(u) of power, may consume an amount 0 <= c(u) <= min(s(u),c_max(u)) of power, and may deliver an amount d(u)=s(u)+p(u)-c(u) of power. The following restrictions apply: c(u)=0 for any power station, p(u)=0 for any consumer, and p(u)=c(u)=0 for any dispatcher. There is at most one power transport line (u,v) from a node u to a node v in the net; it transports an amount 0 <= l(u,v) <= l_max(u,v) of power delivered by u to v. Let Con=Σ_uc(u) be the power consumed in the net. The problem is to compute the maximum value of Con.

An example is in figure 1. The label x/y of power station u shows that p(u)=x and p_max(u)=y. The label x/y of consumer u shows that c(u)=x and c_max(u)=y. The label x/y of power transport line (u,v) shows that l(u,v)=x and l_max(u,v)=y. The power consumed is Con=6. Notice that there are other possible states of the network but the value of Con cannot exceed 6.

Input

There are several data sets in the input. Each data set encodes a power network. It starts with four integers: 0 <= n <= 100 (nodes), 0 <= np <= n (power stations), 0 <= nc <= n (consumers), and 0 <= m <= n^2 (power transport lines). Follow m data triplets (u,v)z, where u and v are node identifiers (starting from 0) and 0 <= z <= 1000 is the value of l_max(u,v). Follow np doublets (u)z, where u is the identifier of a power station and 0 <= z <= 10000 is the value of p_max(u). The data set ends with nc doublets (u)z, where u is the identifier of a consumer and 0 <= z <= 10000 is the value of c_max(u). All input numbers are integers. Except the (u,v)z triplets and the (u)z doublets, which do not contain white spaces, white spaces can occur freely in input. Input data terminate with an end of file and are correct.

Output

For each data set from the input, the program prints on the standard output the maximum amount of power that can be consumed in the corresponding network. Each result has an integral value and is printed from the beginning of a separate line.

Sample Input

2 1 1 2 (0,1)20 (1,0)10 (0)15 (1)20
7 2 3 13 (0,0)1 (0,1)2 (0,2)5 (1,0)1 (1,2)8 (2,3)1 (2,4)7
         (3,5)2 (3,6)5 (4,2)7 (4,3)5 (4,5)1 (6,0)5
         (0)5 (1)2 (3)2 (4)1 (5)4

Sample Output

15
6

Hint

The sample input contains two data sets. The first data set encodes a network with 2 nodes, power station 0 with pmax(0)=15 and consumer 1 with cmax(1)=20, and 2 power transport lines with lmax(0,1)=20 and lmax(1,0)=10. The maximum value of Con is 15. The second data set encodes the network from figure 1.

 

题意:  电网为背景, 给出你节点数和源点,和消耗电力的终点,还有一些节点是中转站不消耗电能.

          问你怎么可以求出最大的输出到全部消耗电力的节点.

 

解题思路:

                1. 网络流问题首先要先设出: 超级源点和超级终点. 我设n为源点,n+1为终点.

                2. 依然采用KM算法求解.

                3. 图论题依然是建图是关键

 

代码：

#include <cstdio>
#include <iostream>
#include <cstring>
#include <queue>
using namespace std;
#define MAX 105
const int INF =(1<<30);

int n, np, nc, m;
int cap[MAX][MAX], flow[MAX][MAX];
int p[MAX];
int a[MAX];

inline int minsize(int a,int b)
{
 return a > b ?  b : a;
}

void read_graph()  //n: 源点. n+1: 终点
{
 int i;
 int u, v, w;
 for(i = 0; i < m; ++i)
 {
  while(getchar() != '(');
  scanf("%d,%d)%d",&u,&v,&w);
  cap[u][v] = w;
 }

 for(i = 0; i < np; ++i)
 {
  while(getchar() != '(');
  scanf("%d)%d",&u,&w);
  cap[n][u] = w;
 }

 for(i = 0; i < nc; ++i)
 {
  while(getchar() != '(');
  scanf("%d)%d",&u,&w);
  cap[u][n+1] = w;
 }
}

int KM()
{
 int result = 0;
 memset(flow,0,sizeof(flow));
 queue<int> qu;

 while(true)
 {
  memset(p,-1,sizeof(p));
  memset(a,0,sizeof(a));
  a[n] = INF;
  qu.push(n);

  while( !qu.empty() )
  {
   int u = qu.front();
   qu.pop();
   for(int v = 0; v < n+2; ++v)
   {
    if(!a[v] && cap[u][v] > flow[u][v])
    {
      p[v] = u;
      qu.push(v);
      a[v] = minsize(a[u],cap[u][v] - flow[u][v]);
    }
   }
  }

  if(a[n+1] == 0) break;

  for(int u = n+1; u != n; u = p[u])
  {
   flow[p[u]][u] += a[n+1];
   flow[u][p[u]] -= a[n+1];
  }

  result += a[n+1];
 }

 return result;
}

int main()
{
// freopen("input.txt","r",stdin);
 while(scanf("%d %d %d %d",&n,&np,&nc,&m) != EOF)
 {
  memset(cap,0,sizeof(cap));
  read_graph();

  printf("%d\n",KM());
 }

 return 0;
}