[网络流24题] 魔术球问题

每日热手题系列
跟最小路径覆盖差不多吧……总觉得输出方案做得很不优美，尤其是用了自己的老板子以后

#include <bits/stdc++.h>
using namespace std;

const int N = 16384, MAX_NODE = 262144;
#define reset(x) memset(x,0,sizeof x)
template <class T> class Graph_Maxflow_Dinic
{
public:
    T tInfinity;
    struct edge
    {
        int p, o;
        T c;
    };
    int s, t;
    T ans=0, tans;
    T dis[MAX_NODE];
    vector <edge> g[MAX_NODE];
    Graph_Maxflow_Dinic()
    {
        tInfinity = 1e+9;
    }
    void make(int p, int q, T c)
    {
        int sz1 = g[p].size(), sz2 = g[q].size();
        edge tmp;
        tmp.p = q;
        tmp.c = c;
        tmp.o = sz2;
        g[p].push_back(tmp);
        tmp.p = p;
        tmp.c = 0;
        tmp.o = sz1;
        g[q].push_back(tmp);
    }
    void reset_graph(int maxnode)
    {
        for (int i = 0; i <= maxnode; i++)
            g[i].clear();
    }
    int dinic_bfs()
    {
        queue<int> q;
        q.push(s);
        memset(dis, 0xff, sizeof dis);
        dis[s] = 1;
        while (q.size())
        {
            int p = q.front();
            q.pop();
            for (int i = 0; i < g[p].size(); i++)
                if (g[p][i].c > 0 && dis[g[p][i].p] < 0)
                    q.push(g[p][i].p),
                           dis[g[p][i].p] = dis[p] + 1;
        }
        return dis[t] > 0;
    }
    T dinic_dfs(int p, T lim)
    {
        T flow = 0;
        if (p == t)
            return lim;
        for (int i = 0; i < g[p].size(); i++)
        {
            if (g[p][i].c > 0 && dis[g[p][i].p] == dis[p] + 1)
            {
                T tmp = dinic_dfs(g[p][i].p, min(lim, g[p][i].c));
                if (tmp > 0)
                {
                    g[p][i].c -= tmp;
                    g[g[p][i].p][g[p][i].o].c += tmp;
                    flow += tmp;
                    lim -= tmp;
                }
            }
        }
        return flow;
    }
    T solve(int src, int tar)
    {
        s = src;
        t = tar;
        tans = 0;
        while (dinic_bfs())
        {
            while (tans = dinic_dfs(s, tInfinity))
            {
                ans += tans;
            }
        }
        return ans;
    }
};

Graph_Maxflow_Dinic <int> g;

int n,t1,t2,t3,t4;

int check(int p,int q)
{
    int t=sqrt(p+q);
    if(t*t==p+q)
        return 1;
    else
        return 0;
}

vector <int> mat[N];
int vis[N];

int main()
{
    cin>>n;
    for(int i=1; i<=n*n*2; i++)
    {
        g.make(1,2*i+1,1);
        g.make(2*i+2,2,1);
        for(int j=1; j<i; j++)
            if(check(i,j))
                g.make(2*i+1,2*j+2,1);
        g.solve(1,2);
        if(i-g.ans > n)
        {
            cout<<i-1<<endl;
            for(int j=0; j<g.g[1].size(); j++)
            {
                int p=g.g[1][j].p;
                for(int k=0; k<g.g[p].size(); k++)
                {
                    if(g.g[p][k].c==0 && g.g[p][k].p>2)
                    {
                        mat[(p-1)/2].push_back((g.g[p][k].p-1)/2);
                        mat[(g.g[p][k].p-1)/2].push_back((p-1)/2);
                    }
                }
            }
            for(int j=1; j<i; j++)
            {
                if(mat[j].size()==1)
                {
                    cout<<j;
                    vis[j]=1;
                    int p=mat[j][0];
                    mat[j].clear();
                    while(mat[p].size()==2)
                    {
                        vis[p]=1;
                        int tmp=p;
                        cout<<" "<<p;
                        if(mat[p][0]==0||mat[mat[p][0]].size()==0)
                            p=mat[p][1];
                        else
                            p=mat[p][0];
                        mat[tmp].clear();
                    }
                    vis[p]=1;
                    cout<<" "<<p;
                    mat[p].clear();
                    cout<<endl;
                }
            }
            for(int j=1; j<i; j++)
                if(!vis[j])
                    cout<<j<<endl;

            return 0;
        }
    }
}

来源：https://www.cnblogs.com/mollnn/p/11724877.html