hihocode#1369 : 网络流一·Ford-Fulkerson算法(EK)

题目链接

最大流模板：求一个有向图的最大流(EK算法)

代码：

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<string>
#include<vector>
#include<stack>
#include<bitset>
#include<cstdlib>
#include<sstream>
#include<cctype>
#include<cmath>
#include<set>
#include<list>
#include<deque>
#include<map>
#include<queue>
using namespace std;
typedef long long ll;
const double PI=acos(-1.0);
const double eps=1e-6;
const int INF=0x7fffffff;
const int maxn=654321;

int T;
int n,m,s,t;
int ans,flag,tot;

int head[maxn],path[maxn],vis[maxn];

struct Edge
{
    int from,to;
    int cap;
    int next;
}e[maxn];

void init()
{
    tot=0;
    s=1;
    t=n;
    memset(head,-1,sizeof(head));
    memset(vis,0,sizeof(vis));
    memset(path,0,sizeof(path));
}

void add_edge(int u,int v,int w)
{
    e[tot].from=u;
    e[tot].to=v;
    e[tot].cap=w;
    e[tot].next=head[u];
    head[u]=tot++;
}

int bfs()
{
    queue<int>q;
    q.push(s);
    vis[s]=1;
    path[s]=-1;
    while(!q.empty())
    {
        int u=q.front();
        q.pop();
        for(int i=head[u];i!=-1;i=e[i].next)
        {
            int v=e[i].to;
            if(e[i].cap>0&&!vis[v])
            {
                path[v]=i;
                vis[v]=1;
                if(v==t)
                    return 1;
                q.push(v);
            }
        }
    }
    return 0;
}

int EK()
{
    int maxFlow=0;
    int flow,i;
    while(bfs())
    {
        memset(vis,0,sizeof(vis));
        i=path[t];
        flow=INF;
        while(i!=-1)
        {
            flow=min(flow,e[i].cap);
            i=path[e[i].from];
        }
        i=path[t];
        while(i!=-1)
        {
            e[i].cap-=flow;
            e[i^1].cap+=flow;
            i=path[e[i].from];
        }
        maxFlow+=flow;
    }
    return maxFlow;
}

int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        init();
        for(int i=0;i<m;i++)
        {
            int a,b,c;
            scanf("%d%d%d",&a,&b,&c);
            add_edge(a,b,c);
            add_edge(b,a,0);
        }
        printf("%d\n",EK());
    }
    return 0;
}