[P1361] 小M的作物 - 最小割

没想到今天早上的第一题网络流就血了这么多发

从经典的二选一问题上魔改 仍然考虑最小割

#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 163840, MAXN = 2602144;
#define reset(x) memset(x,0,sizeof x)
namespace solver {
struct graph {
    int n,m,M,S,T,head[N],cur[N],dep[N],gap[N],q[N];
    long long ans;
    struct ed {
        int to,nxt,val;
    } edge[MAXN];
    void init(int n0,int m0,int S0,int T0) {
        n=n0,m=m0,S=S0,T=T0,M=1,reset(gap);
        reset(head),reset(cur),reset(dep),reset(q);
    }
    void make(int u,int v,int w) {
        edge[++M]=(ed) {v,head[u],w},head[u]=M;
    }
    int dfs(int u,int mx) {
        if (u==T)
            return mx;
        int num=0,f;
        for (int &i=cur[u],v; i; i=edge[i].nxt)
            if (dep[v=edge[i].to]==dep[u]-1 && (f=edge[i].val))
                if (edge[i].val-=(f=dfs(v,min(mx-num,f))), edge[i^1].val+=f, (num+=f)==mx)
                    return num;
        if (!--gap[dep[u]++])
            dep[S]=n+1;
        return ++gap[dep[u]],cur[u]=head[u],num;
    }
    void solve() {
        for (int i=1; i<=n; ++i)
            cur[i]=head[i];
        ans=0;
        for (gap[0]=n; dep[S]<=n; ans+=dfs(S,0x7fffffff));
    }
} g;

int n,m,S,T,t1,t2,t3;

void init() {
    g.init(n,m,S,T);
}

int solve() {
    g.solve();
    return g.ans;
}

void make(int t1,int t2,int t3) {
    g.make(t1,t2,t3);
    g.make(t2,t1,0);
}
} // namespace solver

int n,a[10005],b[10005],m,c[10005][2];

signed main() {
    int ans = 0;
    cin>>n;
    for(int i=1;i<=n;i++) cin>>a[i], ans+=a[i];
    for(int i=1;i<=n;i++) cin>>b[i], ans+=b[i];
    cin>>m;
    solver::n = n+m*2+2;
    solver::S = n+m*2+1;
    solver::T = n+m*2+2;
    solver::init();
    for(int i=1;i<=n;i++) solver::make(n+m*2+1, i, a[i]);
    for(int i=1;i<=n;i++) solver::make(i, n+m*2+2, b[i]);
    for(int i=1;i<=m;i++) {
        int k;
        cin>>k>>c[i][0]>>c[i][1];
        ans += c[i][0] + c[i][1];
        solver::make(n+m*2+1, n+i*2-1, c[i][0]);
        solver::make(n+i*2, n+m*2+2, c[i][1]);
        while(k--) {
            int tmp;
            cin>>tmp;
            solver::make(n+i*2-1,tmp,2e9+10);
            solver::make(tmp,n+i*2,2e9+10);
        }
    }
    cout<<ans - solver::solve()<<endl;
}

原文地址：https://www.cnblogs.com/mollnn/p/12258454.html