BZOJ 2424: [HAOI2010]订货 费用流

2424: [HAOI2010]订货

Description

某公司估计市场在第i个月对某产品的需求量为Ui，已知在第i月该产品的订货单价为di，上个月月底未销完的单位产品要付存贮费用m，假定第一月月初的库存量为零，第n月月底的库存量也为零，问如何安排这n个月订购计划，才能使成本最低？每月月初订购，订购后产品立即到货，进库并供应市场，于当月被售掉则不必付存贮费。假设仓库容量为S。

Input

第1行：n, m, S (0<=n<=50, 0<=m<=10, 0<=S<=10000)

第2行：U1 , U2 , ... , Ui , ... , Un (0<=Ui<=10000)

第3行：d1 , d2 , ..., di , ... , dn (0<=di<=100)

Output

只有1行，一个整数，代表最低成本

Sample Input

3 1 1000
2 4 8
1 2 4

Sample Output

34

HINT

///meek
#include<bits/stdc++.h>
using namespace std ;
typedef long long ll;
#define mem(a) memset(a,0,sizeof(a))
#define pb push_back

const int MAXN = ;
const int MAXM = ;
const int INF = 0x3f3f3f3f;
struct Edge
{
    int to,next,cap,flow,cost;
}edge[MAXM];
int head[MAXN],tol;
int pre[MAXN],dis[MAXN];
bool vis[MAXN];
int N;//节点总个数，节点编号从0~N-1
void init(int n)
{
    N = n;
    tol = ;
    memset(head,-,sizeof(head));
}
void add(int u,int v,int cap,int cost)  //点u至点v,容量，花费
{
    edge[tol].to = v;
    edge[tol].cap = cap;
    edge[tol].cost = cost;
    edge[tol].flow = ;
    edge[tol].next = head[u];
    head[u] = tol++;
    edge[tol].to = u;
    edge[tol].cap = ;
    edge[tol].cost = -cost;
    edge[tol].flow = ;
    edge[tol].next = head[v];
    head[v] = tol++;
}
bool spfa(int s,int t)
{
    queue<int>q;
    for(int i = ;i < N;i++)
    {
        dis[i] = INF;
        vis[i] = false;
        pre[i] = -;
    }
    dis[s] = ;
    vis[s] = true;
    q.push(s);
    while(!q.empty())
    {
        int u = q.front();
        q.pop();
        vis[u] = false;
        for(int i = head[u]; i != -;i = edge[i].next)
        {
            int v = edge[i].to;
            if(edge[i].cap > edge[i].flow &&
               dis[v] > dis[u] + edge[i].cost )
            {
                dis[v] = dis[u] + edge[i].cost;
                pre[v] = i;
                if(!vis[v])
                {
                    vis[v] = true;
                    q.push(v);
                }
            }
        }
    }
    if(pre[t] == -)return false;
    else return true;
}
//返回的是最大流，cost存的是最小费用
int minCostMaxflow(int s,int t,int &cost)
{
    int flow = ;
    cost = ;
    while(spfa(s,t))
    {
        int Min = INF;
        for(int i = pre[t];i != -;i = pre[edge[i^].to])
        {
            if(Min > edge[i].cap - edge[i].flow)
                Min = edge[i].cap - edge[i].flow;
        }
        for(int i = pre[t];i != -;i = pre[edge[i^].to])
        {
            edge[i].flow += Min;
            edge[i^].flow -= Min;
            cost += edge[i].cost * Min;
        }
        flow += Min;
    }
    return flow;
}

const int maxn=+;
const int inff=;

int main()
{
    int n,m,S;
    scanf("%d%d%d",&n,&m,&S);
    int beg=,ends=,x;
    init();
    for(int i=;i<=n;i++) {
        scanf("%d",&x);
        add(i,ends,x,);
    }
    for(int i=;i<=n;i++) {
        scanf("%d",&x);
        add(,i,inff,x);
    }
    for(int i=;i<n;i++) { add(i,i+,S,m); }
    int ans=;
    minCostMaxflow(,ends,ans);
    cout<<ans<<endl;
    return ;
}

代码