POJ 1019 Number Sequence (二分查找+暴力打表)

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <cmath>
#include <stack>
#include <map>
#include <string>
#define LL long long
#define DB double
#define SF scanf
#define PF printf
#define N 100009
#define bug cout<<"bug"<<endl;
using namespace std;
LL sum
;
int re[N*5];
int tmp
;
void init()
{
    int cnt=0;
    int c[10],k;
    for(int i=1;i<N;i++)
    {
        int t = i;
        k = 0;
        while(t>0)
        {
            c[k++]=t%10;
            t/=10;
        }
        sum[i] = sum[i-1]+tmp[i-1]+k;
        tmp[i] = tmp[i-1]+k;
        while(k)
        {
            re[cnt++] = c[--k];
        }
    }
}
int find(LL k)
{
    int l = 0,r=N-1,ret,mid;
    while(l<=r)
    {
        mid = (l+r)>>1;
        if(sum[mid]>k)
        {
            r = mid-1;
        }else
        {
            ret = mid;
            l = mid+1;
        }
    }
    return ret;
}
int main()
{
    #ifndef ONLINE_JUDGE
    freopen("in.txt","r",stdin);
    #endif
    init();
    int n,a;
    SF("%d",&n);
    while(n--)
    {
        SF("%d",&a);
        a--;
        int t = find(a);
        a-=sum[t];
        PF("%d\n",re[a]);
    }
    return 0;
}