BZOJ 最小费用流最大流 1070: [SCOI2007]修车

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string.h>
#include <queue>
#include <vector>
#include <algorithm>
#include <cassert>
#include <set>
#include <map>
#include <cmath>
using namespace std;
#define rep(i,a,b) for(int i=(a);i<(b);++i)
#define rrep(i,a,b) for(int i=(a);i>=(b);--i)
#define clr(a,x) memset(a,(x),sizeof(a));
#define eps 1e-8
#define LL long long
#define mp make_pair
const int inf=1e8;
const int maxn=60*12+5;

struct Edge
{
int u,v,cost,cap,flow;
Edge(int u,int v,int cost,int cap,int flow)
:u(u),v(v),cost(cost),cap(cap),flow(flow) { }
};

vector<Edge> edges;
vector<int> G[maxn];

void add(int u,int v,int cap,int cost)
{
edges.push_back(Edge(u,v,cost,cap,0));
edges.push_back(Edge(v,u,-cost,0,0));
int m=edges.size();
G[u].push_back(m-2);
G[v].push_back(m-1);
}

struct MCMF
{
int p[maxn],d[maxn];
bool inq[maxn];
int s,t,n;

int Augment()
{
int a=inf,x=t;
while(x!=s) {
Edge&e=edges[p[x]];
a=min(a,e.cap-e.flow);
x=e.u;
}
x=t;
while(x!=s) {
edges[p[x]].flow += a;
edges[p[x]^1].flow -= a;
x=edges[p[x]].u;
}
return a;
}

bool spfa(int&flow,int&cost)
{
clr(inq,0);
rep(i,0,n) d[i]=inf;
d[s]=0;
queue<int> q; q.push(s);
while(q.size()) {
int u=q.front(); q.pop();
inq[u]=false;
rep(i,0,G[u].size()) {
Edge&e=edges[G[u][i]];
if(e.cap<=e.flow||d[e.v]<=d[u]+e.cost) continue;
d[e.v]=d[u]+e.cost;
p[e.v]=G[u][i];
if(!inq[e.v]) { inq[e.v]=true; q.push(e.v); }
}
}
if(d[t]==inf) return false;
int a = Augment();
flow += a; cost += d[t]*a;
return true;
}

void init(int n) { this->n=n; }
int mincost(int s,int t)
{
this->s=s; this->t=t;
int flow=0,cost=0;
while(spfa(flow,cost));
return cost;
}
}solver;

int s,t,n,m;
int cost[66][66];
void input()
{
rep(i,0,n) rep(j,0,m) scanf("%d",&cost[i][j]);
rep(i,0,maxn) G[i].clear(); edges.clear();
s=0; t=n*m+n+1;
solver.init(t+1);
rep(i,1,n+1) add(n*m+i,t,1,0);
rep(i,0,m) {
rep(j,1,n+1) {
add(s,i*n+j,1,0);
rep(k,1,n+1) {
add(i*n+j,n*m+k,1,cost[k-1][i]*j);
}
}
}
}

void solve()
{
int cost=solver.mincost(s,t);
printf("%.2lf\n",(double)cost/n);
}

int main()
{
while(scanf("%d%d",&m,&n)==2) {
input();
solve();
}
}