洛谷 2759 奇怪的函数

【题解】

　　取个对数然后二分即可。对于一个数x，x^x的位数就是(int)(lg(x)*x+1).

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<cmath>
 5 #define LL long long
 6 #define rg register
 7 #define N 200010
 8 using namespace std;
 9 int n,l,r,mid;
10 inline int read(){
11     int k=0,f=1; char c=getchar();
12     while(c<'0'||c>'9')c=='-'&&(f=-1),c=getchar();
13     while('0'<=c&&c<='9')k=k*10+c-'0',c=getchar();
14     return k*f;
15 }
16 inline bool check(){
17     long double lg=log10(mid);
18     return lg*mid+1>=n;
19 }
20 int main(){
21     n=read();
22     l=1; r=n;
23     while(l+1<r){
24         mid=(l+r)>>1;
25         if(check()) r=mid; else l=mid;
26     }
27     printf("%d
",r);
28     return 0;
29 }