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;
}