HDU 4430 Yukari's Birthday（二分）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4430

题目大意：给定n个蜡烛，围绕蛋糕的中心插同心圆，从里往外分别是第1圈、第2圈、...第r圈，第 i 圈要插k^i 个蜡烛，且r*k最小。求出r和k。注意，中心点可以放，也可以不放

Sample Input

18

111

1111

Sample Output

1 17

2 10

3 10

代码如下：

 # include<cstdio>
 # include<cstring>
 # include<cmath>
 # include<algorithm>
 # define LL long long
 using namespace std;

 LL pow1(LL a,int b){
     LL ans=;
     for(int i=;i<b;i++)
         ans*=a;
     return ans;
 }
 int main(){
     LL n,r,k;
     while(scanf("%I64d",&n)!=EOF){
         r=;
         k=n-;
         LL left,right,mid;
         for(int i=;i<=;i++){
             left=;
             right=(long long)pow(n,1.0/i);
             while(left<=right){
                 mid=(long long)(left+right)/;
                 LL temp=(mid-pow1(mid,i+))/(-mid);
                 if(temp==n||temp==n-){
                     if(i*mid<r*k){
                         r=i;
                         k=mid;
                     }
                     break;
                 }
                 else if(temp<n) left=mid+;
                 else right=mid-;
             }
         }
         printf("%I64d %I64d\n",r,k);
     }
     return ;
 }