洛谷 P3376【模板】网络最大流

题目描述
如题，给出一个网络图，以及其源点和汇点，求出其网络最大流。

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【题目分析】
网络流模板题目 （Dinic）

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【代码】

#include <cstdio>#include <cstring>#include <cstdlib>#include <cmath>#include <set>#include <map>#include <string>#include <algorithm>#include <vector>#include <iostream>#include <queue>using namespace std;#define maxn 200005#define inf 1000000000int read(){    int x=0,f=1; char ch=getchar();    while (ch<'0'||ch>'9') {if (ch=='-') f=-1; ch=getchar();}    while (ch>='0'&&ch<='9') {x=x*10+ch-'0'; ch=getchar();}    return x*f;}int fr[maxn],to[maxn],ne[maxn],h[maxn],mp[maxn],f[maxn];int n,m,en,S,T;queue <int> q;void add(int a,int b,int r){    fr[en]=a;to[en]=b;ne[en]=h[a];f[en]=r;h[a]=en++;    fr[en]=b;to[en]=a;ne[en]=h[b];f[en]=0;h[b]=en++;}bool tell(){    memset(mp,-1,sizeof mp);    q.push(S); mp[S]=0;    while (!q.empty())    {        int x=q.front();q.pop();        for (int i=h[x];i>=0;i=ne[i])            if (mp[to[i]]==-1&&f[i])            {                mp[to[i]]=mp[x]+1;                q.push(to[i]);            }    }    if (mp[T]==-1) return false;    return true;}int zeng(int k,int now){    if (k==T) return now;    int ret=0;    for (int i=h[k];i>=0&&now>ret;i=ne[i])        if (mp[k]+1==mp[to[i]]&&f[i]!=0)        {            int tmp=zeng(to[i],min(now-ret,f[i]));            f[i]-=tmp; f[i^1]+=tmp; ret+=tmp;        }    if (!ret) mp[k]=-1;    return ret;}int main(){    memset(h,-1,sizeof h);    n=read();m=read();S=read();T=read();    for (int i=1;i<=m;++i)    {        int a=read(),b=read(),c=read();        add(a,b,c);    }    int ans=0,tmp;    while (tell()) while (tmp=zeng(S,inf)) ans+=tmp;    printf("%d\n",ans);}