C++-1019-Number Sequence

 1 #include <set>
 2 #include <map>
 3 #include <cmath>
 4 #include <queue>
 5 #include <vector>
 6 #include <cstdio>
 7 #include <cstdlib>
 8 #include <cstring>
 9 #include <iostream>
10 #include <algorithm>
11 using namespace std;
12 int a[31268],f[31268],b[11],i_b;
13 int digit(int x) {
14     if(x>999999999)return 10;
15     if(x>99999999)return 9;
16     if(x>9999999)return 8;
17     if(x>999999)return 7;
18     if(x>99999)return 6;
19     if(x>9999)return 5;
20     if(x>999)return 4;
21     if(x>99)return 3;
22     if(x>9)return 2;
23     return 1;
24 }
25 int main() {
26     int i,j,k;
27     for(i=1; i<=31267; i++) {
28         for(j=i; j>=1; j--)
29             if(f[j]) {a[i]+=f[j];break;}
30             else a[i]+=digit(j);
31         f[i]=a[i];
32         a[i]+=a[i-1];
33     }//a[31267]=2147378477
34     int T,I;
35     for(scanf("%d",&T); T--;) {
36         scanf("%d",&I);
37         int l=1,r=31267;
38         while(r-l>1) {
39             int mid=(l+r)/2;
40             if(I>a[mid])l=mid;
41             else if(I==a[mid])l=mid,r=mid;
42             else r=mid;
43         }
44         int cnt=I-a[l],num,ans;
45         if(!cnt) {cout<<l%10<<endl;continue;}
46         for(i=l+1; cnt; i++)
47             for(j=1; j<=i && cnt; j++) 
48                 for(num=j,ans=0,k=j; k && cnt; k/=10,cnt--,ans++);
49         for(i_b=0,k=num; k ; b[++i_b]=k%10,k/=10);
50         cout<<b[i_b-ans+1]<<endl;
51     }
52     return 0;
53 }