【codevs1993】草地排水（isap）

来源：互联网发布：js 日期转换时间戳编辑：程序博客网时间：2024/04/26 13:42
题目描述

传送门
题解

网络流最大流模板题
代码

#include<iostream>#include<cstring>#include<cstdio>#include<queue>using namespace std;const int max_n=2005;const int max_m=2005;const int max_e=max_m*2;const int inf=1e9;int point[max_n],next[max_e],v[max_e],remain[max_e],tot;int cur[max_n],deep[max_n],last[max_n],num[max_n];int n,m,x,y,cap,maxflow;queue <int> q;inline void add(int x,int y,int cap){    ++tot; next[tot]=point[x]; point[x]=tot; v[tot]=y; remain[tot]=cap;    ++tot; next[tot]=point[y]; point[y]=tot; v[tot]=x; remain[tot]=0;}inline void bfs(int t){    for (int i=1;i<=n;++i)      deep[i]=n;    deep[t]=0;    while (!q.empty()) q.pop();    q.push(t);    while (!q.empty()){        int now=q.front(); q.pop();        for (int i=point[now];i!=-1;i=next[i])          if (deep[v[i]]==n&&remain[i^1]){            deep[v[i]]=deep[now]+1;            q.push(v[i]);          }    }}inline int addflow(int s, int t) {    int ans=inf,now=t;    while (now!=s) {        ans=min(ans, remain[last[now]]);        now=v[last[now] ^ 1];    }    now=t;    while (now != s) {        remain[last[now]]-=ans;        remain[last[now]^1]+=ans;        now=v[last[now]^1];    }    return ans;}inline void isap(int s,int t){    int now=s;    bfs(t);    for (int i=1;i<=n;++i) ++num[deep[i]];    for (int i=1;i<=n;++i) cur[i]=point[i];    while (deep[s]<n){         if (now==t){            maxflow+=addflow(s,t);            now=s;        }        bool has_find=false;        for (int i=cur[now];i!=-1;i=next[i]){            int u=v[i];            if (deep[u]+1==deep[now]&&remain[i]){                has_find=true;                cur[now]=i;                last[u]=i;                now=u;                break;            }        }        if (!has_find){            int minn=n-1;            for (int i=point[now];i!=-1;i=next[i])              if (remain[i])                minn=min(minn,deep[v[i]]);            if (!(--num[deep[now]])) break;            num[deep[now]=minn+1]++;            cur[now]=point[now];            if (now!=s)              now=v[last[now]^1];        }    }}int main(){    tot=-1;    memset(point,-1,sizeof(point));    memset(next,-1,sizeof(next));    scanf("%d%d",&m,&n);    for (int i=1;i<=m;++i){        scanf("%d%d%d",&x,&y,&cap);        add(x,y,cap);    }    isap(1,n);    printf("%d\n",maxflow);}
0 0