网络流模板

Dinic

#include<stdio.h>
#include<string.h>
#include<iostream>
using namespace std;
const int N=1111,M=1111,INF=0x3f3f3f3f;
struct node
{
    int v,c,next;
}e[M];
int head[N],d[N],q[N];
int n,m,l,r,cnt;
void add(int u,int v,int c)
{
    e[cnt].v=v,e[cnt].c=c;
    e[cnt].next=head[u],head[u]=cnt++;
    e[cnt].v=u,e[cnt].c=0;
    e[cnt].next=head[v],head[v]=cnt++;
}
void init()
{
    memset(head,-1,sizeof(head));
    cnt=0;
}
int bfs(int s,int t)
{
    l=r=0;
    memset(d,-1,sizeof(d));
    q[++r]=s;d[s]=0;int u,v,i;
    while(l<r)
    {
        u=q[++l];
        for(i=head[u];i!=-1;i=e[i].next)
        {
            v=e[i].v;
            if(e[i].c&&d[v]==-1)
            {
                d[v]=d[u]+1;
                q[++r]=v;
            }
        }
    }
    if(d[t]==-1)    return 0;
    return 1;
}
int dfs(int u,int flow)
{
    if(u==t)    return flow;
    int v,a,i,ans=0;
    for(i=head[u];i!=-1;i=e[i].next)
    {
        v=e[i].v;
        if(d[v]==d[u]+1&&e[i].c&&(a=dfs(v,min(flow,e[i].c))))
        {
            e[i].c-=a;
            e[i^1].c+=a;
            ans+=a;
            flow-=a;
            if(!flow)    break;
        }
    }
    if(ans)    return ans;
    d[u]=-1;
    return 0;
}
int dinic(int s,int t)
{
    int ans=0;
    while(bfs(s,t))
        ans+=dfs(s,INF);
    return ans;
}

EK

void updata(int i,int flow)
{
    while(pre[i]!=-1)
    {
        c[i][pre[i]]+=flow;
        c[pre[i]][i]-=flow;
        i=pre[i];
    }
}
int bfs()
{
    memset(p,0,sizeof(p));
    memset(pre,-1,sizeof(pre));
    queue<int> q;
    q.push(1);
    p[1]=1;
    int min_f=1<<28,i,cur;
    while(!q.empty())
    {
        cur=q.front();
        q.pop();
        if(cur==n)
            break;
        for(i=1;i<=n;i++)
        {
            if(c[cur][i]&&!p[i])
            {
                p[i]=1;
                pre[i]=cur;
                min_f=min(min_f,c[cur][i]);
                q.push(i);
            }
        }
    }
    if(pre[n]==-1)
        return 0;
    return min_f;
}
int EK()
{
    int tmp,ans=0;
    do
    {
        tmp=bfs();
        updata(n,tmp);
        ans+=tmp;
    }
    while(tmp!=0);
    return ans;
}

ISAP

#include<stdio.h>
#include<string.h>
#include<iostream>
using namespace std;
#define INF 0x3f3f3f3f

const int N=1100;
const int M=100000;
int h[N],gap[N],head[N];
int cnt,n,m,s,t; 
struct node
{
    int v,c,next;
}e[M];

void init()
{
    memset(head,-1,sizeof(head));
    cnt=0;
}
void add(int u,int v,int w)
{
    e[cnt].v=v,e[cnt].c=w;
    e[cnt].next=head[u];head[u]=cnt++;
    e[cnt].v=u,e[cnt].c=0;
    e[cnt].next=head[v];head[v]=cnt++;
}
int dfs(int u,int flow)
{
    if(u==t)    return flow;
    int c=flow,a,i,v,minh=t;
    for(i=head[u];i!=-1;i=e[i].next)
    {
        if(e[i].c)
        {
            v=e[i].v;
            if(h[v]==h[u]-1)
            {
                a=min(c,e[i].c);
                a=dfs(v,a);
                e[i].c-=a;
                e[i^1].c+=a;
                c-=a;
                if(h[s]>t)  return flow-c;
                if(!c)  break;
            }
            minh=min(minh,h[v]);
        }
    }
    if(c==flow)
    {
        if(--gap[h[u]]==0)    h[s]=t+1;
        h[u]=minh+1;
        ++gap[h[u]];
    }
    return flow-c;
}
int isap() 
{
    memset(gap,0,sizeof(gap));
    memset(h,0,sizeof(h));
    int ans=0;gap[0]=t+1;
    while(h[s]<=t)
        ans+=dfs(s,INF);
    return ans;
}

 笔者建议，ISAP不是那么好理解，如果不能完全理解，又不能使用模板的情况下，请背住DINIC。