URAL - 1233 （计数题目-处理的时候比较麻烦）

#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<string>
#include<cstring>
#include<set>
#include<map>
#include<list>
#include<queue>
#include<vector>
#define tree int o,int l,int r
#define lson o<<1,l,mid
#define rson o<<1|1,mid+1,r
#define lo o<<1
#define ro o<<1|1
#define LL unsigned long long
#define inf 0x7fffffffffffffff
#define eps 1e-7
#define M 9901
#define N 100009
using namespace std;
LL T,n,m,k,t,maxv;
LL f[20];
void init()
{
    f[0]=1;
    for(int i=1; i<20; ++i)
        f[i]=f[i-1]*10ll;
}
LL ok(LL n,LL k)//k的名次
{
    LL t=log10(n)+1;
    LL tk=log10(k)+1;
    LL ans=0;
    for(int i=1; i<=t; i++)
    {
        if(i<=tk)
            ans+=k/f[tk-i]-f[i-1]+1;//加了自己！
        else if(i!=t)
            ans+=k*f[i-tk]-f[i-1];
        else if(k*f[i-tk]<n)
            ans+=k*f[i-tk]-f[i-1];
        else if(k*f[i-tk]>n)
            ans+=n-f[i-1]+1;
        else
            ans+=n-f[i-1];

    }
    return ans;
}
bool check(LL k,LL m)
{
    LL t=log10(k);
    if(k/f[t]==1&&k%f[t]==0&&t+1<m)return 1;
    return 0;
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("ex.in","r",stdin);
#endif
    init();
    while(scanf("%I64d%I64d",&k,&m)==2)
    {
        if(ok(k,k)>m||check(k,m))
        {
            puts("0");
            continue;
        }
        LL l=k,r=inf;
        while(l<r)
        {
            LL mid=(l+r)>>1;
            if(ok(mid,k)<m)
                l=mid+1;
            else
                r=mid;
        }
        printf("%I64d\n",l);
    }
    return 0;
}