P2936(BZOJ3396) [USACO09JAN]全流Total Flow[最大流]

题

裸题不多说，在网络流的练习题里，你甚至可以使用暴力。

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
template<typename T>inline char MIN(T&A,T B){return A<B?A=B,1:0;}
template<typename T>inline char MAX(T&A,T B){return A>B?A=B,1:0;}
template<typename T>inline T _min(T A,T B){return A<B?A:B;}
template<typename T>inline T _max(T A,T B){return A>B?A:B;}
template<typename T>inline T read(T&x){
    x=0;char c;while(!isdigit(c=getchar()))if(isalpha(c))return x=(int)c;
    while(isdigit(c))x=(x<<1)+(x<<3)+(c^48),c=getchar();return x;
}
const int N=1000+7,INF=0x3f3f3f3f;
int w[N<<1],v[N<<1],Next[N<<1],Head[N],cur[N],dis[N],tot=1;
inline void Addedge(int x,int y,int z){
    v[++tot]=y,Next[tot]=Head[x],Head[x]=tot,w[tot]=z;
    v[++tot]=x,Next[tot]=Head[y],Head[y]=tot,w[tot]=0;
}
#define y v[j]
inline char bfs(){
    queue<int> q;memset(dis,0,sizeof dis),dis['A']=1,q.push('A');
    while(!q.empty()){
        int x=q.front();q.pop();
        for(register int j=Head[x];j;j=Next[j])if(w[j]&&!dis[y]){
            dis[y]=dis[x]+1,q.push(y);
            if(y=='Z')return 1;
        }
    }
    return 0;
}
int dinic(int x,int flow){
    if(x=='Z'||!flow)return flow;
    int rest=flow,k;
    for(register int j=cur[x];j&&rest;cur[x]=j,j=Next[j])if(w[j]&&dis[y]==dis[x]+1){
        if(!(k=dinic(y,_min(rest,w[j]))))dis[y]=0;
        rest-=k,w[j]-=k,w[j^1]+=k;
    }
    return flow-rest;
}
#undef y
int m,x,y,z,ans;

int main(){//freopen("tmp.in","r",stdin);freopen("tmp.out","w",stdout);
    read(m);
    for(register int i=1;i<=m;++i)read(x),read(y),read(z),Addedge(x,y,z);
    while(bfs()){
        for(register int i='A';i<='z';++i)cur[i]=Head[i];
        ans+=dinic('A',INF);
    }
    printf("%d
",ans);
    return 0;
}