10706 - Number Sequence

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#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <cctype>
#include <cstdlib>
#include <cmath>
#include <stack>
#define M 31271

using namespace std;

long long a[M];
long long s[M];

int lower_bsearch(int value,long long *A,int x,int y)   //x初始值为 0   y为 len - 1     value为要查找的值，A查找的数组（升序排列）
{
       int mid,max = y;
       while(x < y){
           mid = x + (y-x)/2;

          if(A[mid] >= value)
            y = mid;
           else x = mid + 1;
       }

return x; // 返回第一个大于等于value的值的下标

}

void List()
{
    a[0] = 0;s[0] = 0;
    a[1] = 1;
    s[1] = 1;

    for(int i = 2;i < M;i++)
    {
        a[i] = a[i-1] + (long long)(log10((double)i)) + 1;
        s[i] = s[i-1] + a[i];
    }
}

int Find(int n)
{
    int loc;
    loc = lower_bsearch(n,s,0,M-1); //查找总和在哪个区间段
    int dis = n - s[loc-1];
    int i = lower_bsearch(dis,a,0,M-1);//查找位于哪个数
    int d = dis - a[i-1];
    char ss[100];
    sprintf(ss,"%d",i);
    return (ss[d-1]-'0');
}

int main()
{
//freopen("in.in","r",stdin);

int T,n;

    cin>>T;
    List();
    while(T--)
    {
        cin>>n;
        cout<<Find(n)<<endl;
    }

return 0;
}