费用流

#define MAXN 2002
#define MAXM 500001
#define INF 2147483647
int S,T,n,A,B;
int en,u[MAXM],v[MAXM],first[MAXN],next[MAXM],cap[MAXM],cost[MAXM];//Next Array
bool inq[MAXN];
int d[MAXN]/*spfa*/,p[MAXN]/*spfa*/,a[MAXN]/*可改进量*/;
queue<int>q;
void Init_MCMF(){memset(first,-1,sizeof(first));en=0;S=0;T=(B<<1|1);}
void AddEdge(const int &U,const int &V,const int &W,const int &C)
{u[en]=U; v[en]=V; cap[en]=W; cost[en]=C; next[en]=first[U]; first[U]=en++;
u[en]=V; v[en]=U; cost[en]=-C; next[en]=first[V]; first[V]=en++;}
bool Spfa(int &Flow,int &Cost)
{
    memset(d,0x7f,sizeof(d));
    memset(inq,0,sizeof(inq));
    d[S]=0; inq[S]=1; p[S]=0; a[S]=INF; q.push(S);
    while(!q.empty())
      {
        int U=q.front(); q.pop(); inq[U]=0;
        for(int i=first[U];i!=-1;i=next[i])
          if(cap[i] && d[v[i]]>d[U]+cost[i])
            {
              d[v[i]]=d[U]+cost[i];
              p[v[i]]=i;
              a[v[i]]=min(a[U],cap[i]);
              if(!inq[v[i]]) {q.push(v[i]); inq[v[i]]=1;}
            }
      }
    if(d[T]>2100000000) return 0;
    Flow+=a[T]; Cost+=d[T]*a[T]; int U=T;
    while(U!=S)
      {
        cap[p[U]]-=a[T]; cap[p[U]^1]+=a[T];
        U=u[p[U]];
      }
    return 1;
}
int Mincost()
{
    int Flow=0,Cost=0;
    while(Spfa(Flow,Cost));
    printf("%d %d
",Flow>>1,(-Cost)>>1);
}
int gcd(int a,int b){return b==0?a:gcd(b,a%b);}
int sqr(const int &x){return x*x;}
bool check(const int &a,const int &b)
{
    int t=a*a-b*b;
    if(sqr((int)sqrt(t))!=t) return 0;
    if(gcd(b,(int)sqrt(t))==1) return 1;
    return 0;
}
int main()
{
    scanf("%d%d",&A,&B); Init_MCMF();
    for(int i=A;i<=B;++i)
      for(int j=A;j<i;++j)
        if(check(i,j))
          {
            AddEdge(i,j+B,1,-i-j);
            AddEdge(j,i+B,1,-i-j);
          }
    for(int i=A;i<=B;++i)
      {
        AddEdge(S,i,1,0);
        AddEdge(i+B,T,1,0);
      }
    Mincost();
    return 0;
}