POJ 1019

 1 #include <iostream>
 2 #include<stdio.h>
 3 #include<math.h>
 4 using namespace std;
 5 
 6 const int max = 32000;
 7 unsigned int a[32000], s[32000];
 8 
 9 void prepare()
10 {
11     int i;
12     a[1] = 1;
13     s[1] = 1;
14     for(i=2; i<32000; i++)
15     {
16         a[i] = a[i-1] + (int)(log10((double)i)) + 1;
17         s[i] = s[i-1] + a[i];
18     }
19 }
20 
21 int calc(int number)
22 {
23     int i, location;
24     int length = 0;
25     for(i=1; s[i] < number; i++);
26 
27     //number is in the ith subset
28     location = number - s[i-1];
29 
30     //number is the ith number in ith subset
31     for(i=1; location>length; ++i)
32     {
33         length += (int)(log10((double)i))+1;
34     }
35 
36     //length-location is the redudant numbers for the ith number
37     //for instance: 123, if you want to get 2, length-location would be 1
38     //use 12 mod 10, the result would be 2
39     return (i-1) / (int)(pow((double)10, length-location)) % 10;
40 }
41 
42 int main()
43 {
44     prepare();
45     int count = 0;
46     int number = 0;
47     cin >> count;
48     for(int i = 0; i<count; i++)
49     {
50         cin >> number;
51         cout << calc(number) << endl;
52     }
53 
54 }