POJ1019分块

查询数

11212312341234512345612345671234567812345678912345678910123456789101112345678910.......

第n（<= 2147483647）个数字是多少。

分块思想：

typedef long long LL ;

const int  maxn = 40000 ;
LL   sum[maxn+8] , x[maxn+8] ;

int  main(){
     int i  , j ;
     sum[0] = x[0] = 0 ;
     for(i = 1 ; i <= 9 ; i++)  x[i] = x[i-1] + 1 ;
     for(i = 10 ; i <= 99 ; i++)  x[i] = x[i-1] + 2 ;
     for(i = 100 ; i <= 999 ; i++)  x[i] = x[i-1] + 3 ;
     for(i = 1000 ; i <= 9999 ; i++) x[i] = x[i-1] + 4 ;
     for(i = 10000 ; i <= 40000 ; i++) x[i] = x[i-1] + 5 ;
     for(i = 1 ; i <= 40000 ; i++) sum[i] = sum[i-1] + x[i] ;
     int t ; LL n ;
     cin>>t ;
     while(scanf("%lld" , &n) != EOF){
          i = lower_bound(sum , sum+40000 , n) - sum ;
          n -= sum[i-1] ;
          i = lower_bound(x , x+i+1 , n) - x ;
          n -= x[i-1] ;
          vector<int> dig ; dig.clear() ;
          while(i){
               dig.push_back(i % 10) ;
               i /= 10 ;
          }
          std::reverse(dig.begin() , dig.end()) ;
          cout << dig[n-1] << endl ;
     }
     return 0 ;
}