luogu2053 [SCOI2007]修车

把m个师傅拆成n个阶段，考虑每个人选上第某个阶段的某师傅对答案做出的贡献。

参见这里与那里。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
using namespace std;
int m, n, uu, cnt, hea[605], ss, tt, minCost, dis[605], pre[605];
bool vis[605];
queue<int> d;
struct Edge{
	int too, nxt, val, cst;
}edge[100005];
void add_edge(int fro, int too, int val, int cst){
	edge[cnt].nxt = hea[fro];
	edge[cnt].too = too;
	edge[cnt].val = val;
	edge[cnt].cst = cst;
	hea[fro] = cnt++;
}
void addEdge(int fro, int too, int val, int cst){
	add_edge(fro, too, val, cst);
	add_edge(too, fro, 0, -cst);
}
bool bfs(){
	memset(pre, -1, sizeof(pre));
	memset(dis, 0x3f, sizeof(dis));
	dis[ss] = 0;
	d.push(ss);
	vis[ss] = true;
	while(!d.empty()){
		int x=d.front();
		d.pop();
		vis[x] = false;
		for(int i=hea[x]; i!=-1; i=edge[i].nxt){
			int t=edge[i].too;
			if(dis[t]>dis[x]+edge[i].cst && edge[i].val>0){
				dis[t] = dis[x] + edge[i].cst;
				pre[t] = i;
				if(!vis[t]){
					vis[t] = true;
					d.push(t);
				}
			}
		}
	}
	return dis[tt]!=0x3f3f3f3f;
}
void dinic(){
	while(bfs()){
		int tmp=0x3f3f3f3f;
		for(int i=pre[tt]; i!=-1; i=pre[edge[i^1].too])
			tmp = min(tmp, edge[i].val);
		for(int i=pre[tt]; i!=-1; i=pre[edge[i^1].too]){
			edge[i].val -= tmp;
			edge[i^1].val += tmp;
			minCost += tmp * edge[i].cst;
		}
	}
}
int main(){
	memset(hea, -1, sizeof(hea));
	cin>>m>>n;
	ss = 0; tt = m * n + n + 1;
	for(int i=1; i<=n; i++)
		for(int j=1; j<=m; j++){
			scanf("%d", &uu);
			for(int k=1; k<=n; k++)
				addEdge(i, j*n+k, 1, uu*k);
		}
	for(int i=1; i<=n; i++)
		addEdge(ss, i, 1, 0);
	for(int i=1; i<=m; i++)
		for(int j=1; j<=n; j++)
			addEdge(i*n+j, tt, 1, 0);
	dinic();
	printf("%.2lf\n", (double)minCost/n);
	return 0;
}