UVA 10746 Crime Wave - The Sequel

最新推荐文章于 2015-08-16 13:32:45 发布

转载最新推荐文章于 2015-08-16 13:32:45 发布 · 160 阅读

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原文链接：http://www.cnblogs.com/Commence/p/4022027.html

本文深入探讨了最小费用最大流算法的实现细节，通过具体的代码示例展示了如何构建网络流图，设置流量和成本，并迭代求解最优解。特别关注了从源点到汇点的路径选择，以及如何调整流量以达到最小总成本。

最小费用最大流源点->警察->bank->汇点

剩下的模板就可以

#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <stack>
#include <queue>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#define LL long long
#define PI 3.1415926535897932626
using namespace std;
int gcd(int a, int b) {return a % b == 0 ? b : gcd(b, a % b);}
#define MAXN 50
#define INF 100000000
const double eps = 1e-9 ;
int flow[MAXN][MAXN],cap[MAXN][MAXN];
double cost[MAXN][MAXN];
int N,M,src,tag;
double c;
int ans;
void read()
{
    memset(cap,0,sizeof(cap));
    memset(flow,0,sizeof(flow));
    for (int i = 0; i < MAXN; i++) for (int j = 0; j < MAXN; j++) cost[i][j] = INF;
    src = 0 ; tag = N + M + 1;
    for (int i = 1; i <= M; i++) {cap[0][i] = 1; cost[0][i] = 0;}
    for (int i = 1; i <= N; i++) {cap[M + i][tag] = 1; cost[M + i][tag] = 0;}
    for (int i = 1; i <= N; i++)
        for (int j = 1; j <= M; j++)
    {
        double tmp;
        scanf("%lf",&tmp);
        cost[j][i + M] = tmp;
        cost[i + M][j] = -tmp;
        cap[j][i + M] = 1;
    }
}
void slove()
{
    queue<int>q;
    bool inq[MAXN];
    int p[MAXN];
    double d[MAXN];
    ans = 0;
    c = 0.0;
    while (true)
    {
        memset(inq,false,sizeof(inq));
        for (int i = 0; i < MAXN; i ++) d[i] = INF;
        d[src] = 0;
        q.push(src);
        while (!q.empty())
        {
            int u = q.front(); q.pop();
            inq[u] = false;
            for (int v = 0 ; v <= tag; v++)
              if (cap[u][v] > flow[u][v] && d[v] > d[u] + cost[u][v] + eps)
              {
                  d[v] = d[u] + cost[u][v];
                  p[v] = u;
                  if (!inq[v])
                  {
                      inq[v] = true;
                      q.push(v);
                  }
              }
        }
        if (d[tag] == INF)  break;
        int a = INF;
        for (int u = tag; u != src; u = p[u])  a = min(a,cap[p[u]][u] - flow[p[u]][u]);
        for (int u = tag; u != src; u = p[u])
        {
            flow[p[u]][u] += a;
            flow[u][p[u]] -= a;
        }
        c += d[tag] * a;
        ans += a;
    }
}
int main()
{
    //freopen("sample.txt","r",stdin);
    //freopen("output.txt","w",stdin);
    while (scanf("%d%d",&N,&M) != EOF)
    {
        if (N == 0 && M == 0) break;
        read();
        slove();
        printf("%.2lf\n",c / N + eps);
    }
    return 0;
}

转载于:https://www.cnblogs.com/Commence/p/4022027.html