网络流 EK算法

#include <iostream>
#include <queue>
#include <algorithm>
#include <cstdio>
#include <cstring>
#define maxn 205
using namespace std;
const int inf=1e9;
int mp[maxn][maxn]={0};
int pre[maxn]={0};
bool vis[maxn]={0};
int n;
bool bfs(int s,int t)
{
    queue<int> q;
    memset(vis,false,sizeof(vis));
    memset(pre,-1,sizeof(pre));
    vis[s]=true;
    pre[s]=s;
    q.push(s);
    while(!q.empty())
    {
        int now=q.front();
        q.pop()
        for(int i=1;i<=n;i++)
        {
            if(mp[now][i]&&!vis[i])
            {
                vis[i]=true;
                pre[i]=now;
                if(i==t) return true;
                q.push(i);
            }
        }
    }
    return false;
}
int ek(int s,int t)
{   int ans=0,i;
    while(bfs(s,t))
    {   int minum=inf;
        for(i=t;i!=s;i=pre[i])
        {
            minum=min(minum,mp[pre[i]][i]);
        }
        for(i=t;i!=s;i=pre[i])
        {
            mp[pre[i]][i]-=minum;
            mp[i][pre[i]]+=minum;
        }
        ans+=minum;
    }
    return ans;
}
int main()
{
    int t;
    while(~scanf("%d%d",&t,&n))
    {   memset(mp,0,sizeof(mp));
        while(t--)
    {

        int x,y,z;
        cin>>x>>y>>z;
        mp[x][y]+=z;
    }
    cout<<ek(1,n)<<endl;}

    return 0;
}

　　2.邻接表实现

#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>
#define maxn 2005
using namespace std;
typedef long long ll;
struct edge
{
    int u;
    int v;
    int w;
    int next;
}edge[maxn];
struct node
{
    int v,id;
};
int cnt=0;
int head[maxn];
void addedge(int u,int v,int w)
{
    edge[cnt].u=u;
    edge[cnt].v=v;
    edge[cnt].w=w;
    edge[cnt].next=head[u];
    head[u]=cnt++;
}
node pre[maxn];
bool vis[maxn]={0};
bool bfs(int s,int t)
{
    memset(vis,false,(sizeof(vis)));
    memset(pre,-1,sizeof(pre));
    queue<int> q;
    q.push(s);
    vis[s]=true;
    while(!q.empty())
    {
        int u=q.front();
        q.pop();
        for(int i=head[u];i!=-1;i=edge[i].next)
        {
            int v=edge[i].v;
            if(!vis[v]&&edge[i].w)
            {
                pre[v].v=u;
                pre[v].id=i;
                vis[v]=true;
                if(v==t) return true;
                q.push(v);
            }
        }
    }
    return false;
}
int ek(int s,int t)
{   int ans=0,i;
    while(bfs(s,t))
    {   int minum=1e9;
        for(i=t;i!=s;i=pre[i].v)
        {
            minum=min(minum,edge[pre[i].id].w);
        }
        for(i=t;i!=s;i=pre[i].v)
        {
            edge[pre[i].id].w-=minum;
            edge[pre[i].id^1].w+=minum;
        }
        ans+=minum;
    }
    return ans;
}
int main()
{

    int n,m,i;
    while(cin>>m>>n)
    {
        memset(head,-1,sizeof(head));
        memset(edge,0,sizeof(edge));
        for(i=1;i<=m;i++)
    {
        int u,v,w;
        cin>>u>>v>>w;
        addedge(u,v,w);
        addedge(v,u,0);
    }
    cout<<ek(1,n)<<endl;
    }
    return 0;
}