poj3422 来一道费用流

来源：互联网发布：剃头理发器软件编辑：程序博客网时间：2024/06/06 07:39
题目链接
poj3422
真是感觉网络流越来越神奇了。
1、最小费用流 -- 最大费用流之间转化
2、拆点
3、费用 OR 流量 (cost, flow)
#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#include <vector>#include <cmath>#include <queue>#include <stack>#include <map>#include <set>using namespace std;#define clr(x) memset(x,0,sizeof(x))#define fp1 freopen("in.txt","r",stdin)#define fp2 freopen("out.txt","w",stdout)#define pb push_back#define INF 0x3c3c3c3ctypedef long long LL;//网络中可以有负权边，但不能有负权圈。//每次先调用init(); 初始maxn、INF之类。//Addedge(cap, flow):cap是容量,flow是流量。const int maxn = 100000;struct Edge{    int from, to, cap, flow, cost;};struct MCMF{    int n, m, s, t;    vector<Edge> edges;    vector<int> G[maxn];    int inq[maxn];      //是否在队列中    int d[maxn];        //Bellman-Ford    int p[maxn];        //上一条弧    int a[maxn];        //可改进量    void init(int n)    //感觉每次调用都要调用init初始化哪    {        this->n = n;        for(int i = 0;i < n;i++) G[i].clear();        edges.clear();        //clr(p); clr(a);  clr(d);    }    void addedge(int from, int to, int cost, int cap)    {        edges.pb((Edge){from, to, cap, 0, cost});        edges.pb((Edge){to, from, 0, 0, -cost});        m = edges.size();        G[from].pb(m-2);        G[to].pb(m-1);    }    //其他成员函数    bool spfa(int s, int t, int &flow, int &cost)    {        for(int i = 0;i < n;i++) d[i] = INF;        clr(inq);        d[s] = 0;  inq[s] = 1;  p[s] = 0;  a[s] = INF;        queue<int> Q;        Q.push(s);        while(!Q.empty()){            int u = Q.front();  Q.pop();            inq[u] = 0;            for(int i = 0;i < G[u].size();i++){                Edge &e = edges[G[u][i]];                if(e.cap>e.flow && d[e.to]>d[u]+e.cost){                    d[e.to] = d[u] + e.cost;                    p[e.to] = G[u][i];                    a[e.to] = min(a[u], e.cap-e.flow);                    if(!inq[e.to]){                        Q.push(e.to);  inq[e.to] = 1;                    }                }            }        }        if(d[t] == INF) return false;  //s-t不连通，失败退出        flow += a[t];        cost += d[t]*a[t];        int u = t;        while(u != s){            edges[p[u]].flow += a[t];            edges[p[u]^1].flow -= a[t];            u = edges[p[u]].from;        }        return true;    }    int Mincost(int s, int t)    {        int flow = 0, cost = 0;        while(spfa(s, t, flow, cost));        return cost;    }};MCMF flow;int map1[55][55];int main(){    //freopen("in.txt", "r", stdin);    int n, m;    while (scanf("%d %d", &n, &m) == 2) {        flow.init(n*n*2+100);int i, j;for (int i=1; i <= n;i++) {for (int j=1; j <= n;j++) {scanf("%d", &map1[i][j]);}}for (i = 1; i <= n; i++) {for (j = 1; j <= n; j++) {int u = (i - 1) * n + j;flow.addedge(u, n*n+u, -map1[i][j], 1); //reversed                flow.addedge(u, n*n+u, 0, m-1);if(j != n){                    flow.addedge(u, u+1, 0, m);                    flow.addedge(n*n+u, u+1, 0, m);}if(i != n){                    flow.addedge(u, u+n, 0, m);                    flow.addedge(n*n+u, u+n, 0, m);}}}flow.addedge(0, 1, 0, m);                 //SuperSourceflow.addedge(n*n*2, n * n * 2 + 1, 0, m); //SuperSink        cout<<-flow.Mincost(0, n*n*2+1);}    return 0;}
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