BZOJ 2324: [ZJOI2011]营救皮卡丘(带上下限的最小费用最大流)

这道题么= =还是有些恶心的，第一次写带上下界的网络流，整个人都萌萌哒~~~

首先先预处理得最短路后

直接用费用流做就行了。

第一次写，还是挺好写的= =

CODE：

#include<cstdio>

#include<iostream>

#include<algorithm>

#include<cstring>

#include<queue>

using namespace std;

#define maxn 310

#define maxm 100000

struct edges{

    int to,next,cap,dist;

}edge[maxm];

int next[maxn],l;

void addedge(int x,int y,int z,int d){

    l++;

    edge[l*2]=(edges){y,next[x],z,d};next[x]=l*2;

    edge[l*2+1]=(edges){x,next[y],0,-d};next[y]=l*2+1;

}

int inf;

int dist[maxn],w[maxn],s,t,cnt;

bool b[maxn];

queue<int> q;

bool spfa() {

    for (int i=1;i<=cnt;i++) dist[i]=inf;

    dist[s]=0;

    q.push(s);

    while (!q.empty()) {

        int u=q.front();q.pop();

        b[u]=0;

        for (int i=next[u];i;i=edge[i].next)

            if (edge[i].cap&&edge[i].dist+dist[u]<dist[edge[i].to]) {

                dist[edge[i].to]=dist[u]+edge[i].dist;

                w[edge[i].to]=i;

                if (!b[edge[i].to]) {

                    b[edge[i].to]=1;

                    q.push(edge[i].to);

                }

            }

    }

    return dist[t]!=inf;

}

int ans;

int mcmf(int ss,int tt){

    s=ss,t=tt;

    while (spfa()) {

        int x=t,flow=inf;

        while (x!=s) {

            flow=min(flow,edge[w[x]].cap);

            x=edge[w[x]^1].to;

        }

        ans+=flow*dist[t];

        x=t;

        while (x!=s) {

            edge[w[x]].cap-=flow;

            edge[w[x]^1].cap+=flow;

            x=edge[w[x]^1].to;

        }

    }

}

int dis[maxn][maxn],f[maxn][maxn],id[maxn][2];

int main(){

    int n,m,k;

    scanf("%d%d%d",&n,&m,&k);

    memset(f,10,sizeof(f));

    inf=f[0][0];

    for (int i=1;i<=m;i++) {

        int x,y,z;

        scanf("%d%d%d",&x,&y,&z);

        f[x][y]=f[y][x]=min(f[x][y],z);

    }

    for (int i=0;i<=n;i++) f[i][i]=0;

    for (int k=0;k<=n;k++) {

        for (int i=0;i<=n;i++)

                for (int j=0;j<=n;j++)

                    f[i][j]=min(f[i][j],f[i][k]+f[k][j]);

        for (int i=0;i<=n;i++) dis[i][k]=f[i][k];

    }

    for (int i=0;i<=n;i++) id[i][0]=++cnt;

    for (int i=0;i<=n;i++) id[i][1]=++cnt;

    int s=++cnt,t=++cnt;

    addedge(id[0][0],id[0][1],k,0);

    for (int i=1;i<=n;i++) {

        addedge(id[0][1],id[i][0],inf,dis[0][i]);

        addedge(id[i][1],id[n][1],inf,0);

        addedge(id[i][0],id[i][1],inf,0);

        addedge(s,id[i][1],1,0);

        addedge(id[i][0],t,1,0);

    }

    for (int i=0;i<n;i++)

        for (int j=i+1;j<=n;j++)

           if (dis[i][j]!=inf) addedge(id[i][1],id[j][0],inf,dis[i][j]);

    addedge(id[n][1],id[0][0],inf,0);

    mcmf(s,t);

    next[s]=next[t]=0;

    next[id[n][1]]=edge[next[id[n][1]]].next;

    next[id[0][0]]=edge[next[id[0][0]]].next;

    mcmf(id[0][0],id[n][1]);

    printf("%d ",ans);

    return 0;

}