Hrbeu 5012(二分逼近)

 

比较恶心的逼近 首先对2组数据排序

 

然后在形式上化作N*N的阵 使用DP变量保存查找深度

 

每次查询如果key值较小 左移一次 则排名增加(n-dp) 否则深度+1

 

使用二分逼近 返回ans 注意逼近时计算k的上下界

 

代码如下: 

 

 

#include  < iostream >
#include  < algorithm >
using   namespace  std;

long  A[ 10010 ];
long  B[ 10010 ];
long  N,K;

bool  check( long  key)
{
     long  i;
     long  rank = 1 ;
     long  dp = 0 ;

     for  (i = N - 1 ;i >= 0 && dp <= N;)
    {
         if  (key < A[i] * B[dp])
        {
            rank += (N - dp);
             if  (rank > K)
            {
                 return   false ;
            }
             -- i;
        }
         else
        {
             ++ dp;
        }
    }

     long  up = rank;

    rank = 1 ;
    dp = 0 ;
     for  (i = N - 1 ;i >= 0 && dp <= N;)
    {
         if  (key <= A[i] * B[dp])
        {
            rank += (N - dp);
             if  (rank > K)
            {
                 return   false ;
            }
             -- i;
        }
         else
        {
             ++ dp;
        }
    }

     long  down = rank;


     return  rank >= up && rank <= down;
}

int  main()
{
     long  T;
    scanf( " %ld " , & T);

     while  (T -- )
    {
         long  i;

        scanf( " %ld %ld " , & N, & K);

         for  (i = 0 ;i < N; ++ i)
        {
            scanf( " %ld " , & A[i]);
        }

         for  (i = 0 ;i < N; ++ i)
        {
            scanf( " %ld " , & B[i]);
        }

        sort(A,A + N);
        sort(B,B + N);


         long  low = A[ 0 ] * B[ 0 ];
         long  high = A[N - 1 ] * B[N - 1 ];

         long  h = low,r = high,mid,ans = h;

         while (h <= r)
        {
            mid = (h + r) >> 1 ;
             if ( ! check(mid))
            {
                ans = mid;
                h = mid + 1 ;
            }
             else
            {
                r = mid - 1 ;
            }
        }

        printf( " %ld\n " ,ans);



    }
     return   0 ;
}