Ural 1057

刘聪  集训队里面的一篇文章 （浅谈数位统计）如果大于1  后面的所有位都变成1  这是满足条件的能到达的最大值

#include<iostream>
#include<stdio.h>
#include<cstring>
#include<algorithm>
using namespace std;

int X,Y,K,B,arr[33],F[33][33];
int work( int num )
{
       int i,j,t = num,k = 0;
       while( t )
       {
           arr[k++] = t%B;
           t /= B;
       }
       for( i = k-1; i >= 0 ; i-- )
       if( arr[i] > 1 )
       {
             for( j = i; j >= 0; j-- )
               arr[j] = 1;
             break;
       }
         num = 0;
       for( i = k-1; i>= 0 ; i-- )
       if( arr[i] )
       num += (1<<i);

       int ans = 0,total = 0;
       for( i = 31; i; i-- )
       {
            if( num&(1<<i) )
            {
                total++;
                if( total > K )break;
                num^=(1<<i);
            }
            if( (1<<(i-1)) <= num )
            ans += F[i-1][K-total];
        }
        if( num + total == K )ans++;
        return ans;
}
int main( )
{
      F[0][0] = 1;
      for( int i = 1; i <=32; i++ )
      {
          F[i][0] = 1;
          for( int j = 1; j <= i; j++ )
          F[i][j] = F[i-1][j] + F[i-1][j-1];
      }
      while( scanf("%d%d%d%d",&X,&Y,&K,&B) != EOF )
      printf("%d\n",work( Y ) - work( X - 1 ) );
      return 0;
}
/*

123  312312
3 3
0 321321
3 4
1232  32131321
2 3


901
936
247
*/