板子题

当前弧优化版本

目前效率最高

//#pragma comment(linker, "/stack:200000000")
//#pragma GCC optimize("Ofast,no-stack-protector")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
//#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define pi acos(-1.0)
#define ll long long
#define vi vector<int>
#define mod 1000000007
#define C 0.5772156649
#define ls l,m,rt<<1
#define rs m+1,r,rt<<1|1
#define pil pair<int,ll>
#define pli pair<ll,int>
#define pii pair<int,int>
#define cd complex<double>
#define ull unsigned long long
#define base 1000000000000000000
#define fio ios::sync_with_stdio(false);cin.tie(0)using namespace std;const double g=10.0,eps=1e-12;
const int N=200+10,maxn=10000+10,inf=0x3f3f3f3f,INF=0x3f3f3f3f3f3f3f3f;struct edge{
    int to,Next,c;
}e[maxn];
int s,t,cnt,head[N],cur[N];
int n,m;
void init()
{
    cnt=0;
    memset(head,-1,sizeof head);
}
void add(int u,int v,int c)
{
    e[cnt].to=v;
    e[cnt].c=c;
    e[cnt].Next=head[u];
    head[u]=cnt++;
    e[cnt].to=u;
    e[cnt].c=0;
    e[cnt].Next=head[v];
    head[v]=cnt++;
}
int dis[N];
bool bfs()
{
    queue<int>q;
    memset(dis,-1,sizeof dis);
    dis[s]=1;
    q.push(s);
    while(!q.empty())
    {
        int x=q.front();q.pop();
        for(int i=head[x];~i;i=e[i].Next)
        {
            int y=e[i].to;
            if(dis[y]==-1&&e[i].c>0)
            {
                dis[y]=dis[x]+1;
                q.push(y);
            }
        }
    }
    return dis[t]!=-1;
}
ll dfs(int u,ll mx)
{
    if(u==t)return mx;
    ll flow=0,f;
    for(int &i=cur[u];~i;i=e[i].Next)
    {
        int x=e[i].to;
        if(dis[x]==dis[u]+1&&e[i].c>0&&(f=dfs(x,min(mx-flow,1ll*e[i].c))))
        {
            e[i].c-=f;
            e[i^1].c+=f;
            flow+=f;
            if(flow == mx) break;
        }
    }
    if(flow==0)dis[u]=-2;
    return flow;
}
ll maxflow()
{
    ll ans=0,f;
    while(bfs())
    {
        for(int i=0;i<=n;i++)cur[i]=head[i];
        while((f=dfs(s,inf)))ans+=f;
    }
    return ans;
}
int main()
{
    init();
    scanf("%d%d%d%d",&n,&m,&s,&t);
    for(int i=0;i<m;i++)
    {
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        add(a,b,c);
    }
    printf("%lld\n",maxflow());
    return 0;
}