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;

}

巴特西

luogu2053 [SCOI2007]修车

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