hdu 1532Drainage Ditches

来源：互联网发布：java基础入门编辑：程序博客网时间：2024/05/20 10:15

网络流！

1. E_K()

#include <iostream>#include<queue>#include<cstring>#include<cstdlib>using namespace std;int g[205][205];int n,m;queue<int> q;int parent[205];int vis[205];int flow[205];int min(int a,int b){    return a>b?b:a;}int bfs(){    while(!q.empty()) q.pop();    for(int i=0;i<=m;i++)        flow[i]=vis[i]=0;    flow[1]=100000000;    q.push(1);    vis[1]=1;    while(!q.empty())    {        int cur=q.front();        q.pop();        if(cur==m)            return flow[cur];        for(int i=2;i<=m;i++)            if(!vis[i]&&g[cur][i])            {                vis[i]=1;                q.push(i);                parent[i]=cur;                flow[i]=min(flow[cur],g[cur][i]);            }    }    return 0;}int E_K(){    int all=0,add=0;    parent[1]=0;    while((add=bfs()))    {        all+=add;        int now=m,pre;        while((pre=parent[now]))        {            g[pre][now]-=add;            g[now][pre]+=add;            now=pre;        }    }    return all;}int main(){//    freopen("in.txt","r",stdin);    while(scanf("%d %d",&n,&m)==2)    {        for(int i=0;i<=m;i++)            for(int j=0;j<=m;j++)                g[i][j]=0;        for(int i=0;i<n;i++)        {            int s,e,c;            scanf("%d %d %d",&s,&e,&c);            g[s][e]+=c;        }        int t=0;        printf("%d\n",E_K());    }    return 0;}

2. Dinic()

#include <iostream>#include<queue>#include<cstring>#include<cstdlib>using namespace std;int g[205][205];int n,m;int layer[205];queue<int> q;int min(int a,int b){    return a>b?b:a;}int bfs(){    for(int i=0;i<=m;i++)        layer[i]=-1;    while(!q.empty()) q.pop();    q.push(1);    layer[1]=0;    while(!q.empty())    {        int cur=q.front();        q.pop();        if(cur==m)            return 1;        for(int i=2;i<=m;i++)            if(layer[i]==-1&&g[cur][i])            {                layer[i]=layer[cur]+1;                q.push(i);            }    }    return 0;}int dfs(int cur,int flow){    if(cur==m) return flow;    for(int i=2;i<=m;i++)        if((layer[i]==layer[cur]+1)&&g[cur][i])        {            int t=dfs(i,min(flow,g[cur][i]));            if(t)            {                g[cur][i]-=t;                g[i][cur]+=t;                return t;            }        }    return 0;}int dinic(){    int all=0,t;    while(bfs())        while(t=dfs(1,100000000))            all+=t;    return all;}int main(){//    freopen("in.txt","r",stdin);    while(scanf("%d %d",&n,&m)==2)    {        for(int i=0;i<=m;i++)            for(int j=0;j<=m;j++)                g[i][j]=0;        for(int i=0;i<n;i++)        {            int s,e,c;            scanf("%d %d %d",&s,&e,&c);            g[s][e]+=c;        }        int t=dinic();        printf("%d\n",t);    }    return 0;}