Number Sequence POJ 1019

 1 #include <iostream>
 2 using namespace std;
 3 
 4 long long int pow(long long int base, long long int exp)
 5 {
 6     long long int result = 1;
 7     for(long long int i = 0; i < exp; i++) {
 8         result *= base;
 9     }
10     return result;
11 }
12 
13 int find(long long pos)
14 {
15     long long sum = 0, last_sum = 0;
16     int k = 1;
17     int result = 0;
18     
19     while(true) {
20         last_sum = sum;
21         sum += 9 * pow(10, k-1) * k;
22         if(sum > pos) {
23             long long diff = pos - last_sum;
24             long long rank = diff / k;
25             long long mod = diff % k;
26             if(k == 1) result = diff + 1;
27             else result = ((pow(10, k-1) + rank)/pow(10, k-1-mod)) % 10;
28             break; 
29         }
30         k++;
31     }
32     
33     return result;
34 }
35 
36 int main()
37 {
38     int t;
39     long long i, group_num, member_size, sum, last_sum, last_group_sum, group_sum, pos, res;
40     cin >> t;
41     for(int j = 0; j < t; j++) {
42         group_num = 1;
43         last_group_sum = 0;
44         member_size = 1;
45         sum = 0;
46         cin >> i;
47         i = i - 1;
48         while(true){
49             last_sum = sum;
50             group_sum = last_group_sum + member_size;
51             sum += group_sum;
52             if(sum > i) {
53                 res = find(i - last_sum);
54                 cout<<res<<endl;
55                 break;
56             }
57             last_group_sum = group_sum;
58             group_num++;
59             if(group_num/pow(10, member_size) - (group_num-1)/pow(10, member_size) == 1) member_size++;
60         }
61     }
62     return 0;
63 }