Consider two integer sequences f(n) = n! and g(n) = an, where n is a positive integer. For any integer a > 1 the second sequence is greater than the first for a finite number of values. But starting from some integer k, f(n) is greater than g(n) for all n >= k. You are to find the least positive value of n for which f(n) > g(n), for a given positive integer a > 1.
Input
The first line of the input contains number t – the amount of tests. Then t test descriptions follow. Each test consist of a single number a.
Constraints
1 <= t <= 100000
2 <= a <= 106
Output
For each test print the least positive value of n for which f(n) > g(n).
Example
Input: 3 2 3 4 Output: 4 7 9
有很多组询问,给个常数1<=a<=100w,求使得n! > a^n 的最小整数n
构造f(n)=n!,g(n)=a^n,a是常数,由高中知识就很容易知道f(n)趋近极限的速度最后会更快
不妨令h(n)=f(n)-g(n),则h(n)应当是递增的(吧?)
只要求h(n)=(n!-a^n) > 0的最小n
因此可知当a增加的时候,h(n)的零点应当也是增加的
所以可以枚举个a的值,不断增加n的值,只要n!>a^n,即log(n!)>nloga
即log1+log2+...+logn>nloga
左边的部分可以在枚举a的时候顺便求得
1 #include<cstdio> 2 #include<iostream> 3 #include<cstring> 4 #include<cstdlib> 5 #include<algorithm> 6 #include<cmath> 7 #include<queue> 8 #include<deque> 9 #include<set> 10 #include<map> 11 #include<ctime> 12 #define LL long long 13 #define inf 0x7ffffff 14 #define pa pair<int,int> 15 #define mkp(a,b) make_pair(a,b) 16 #define pi 3.1415926535897932384626433832795028841971 17 using namespace std; 18 inline LL read() 19 { 20 LL x=0,f=1;char ch=getchar(); 21 while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} 22 while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();} 23 return x*f; 24 } 25 int n; 26 int ans[1000010]; 27 int main() 28 { 29 double s=0;int t=1; 30 for (int i=1;i<=1000000;i++) 31 { 32 while (s<=t*log(i)){t++;s+=log(t);} 33 ans[i]=t; 34 } 35 int T=read(); 36 while (T--){printf("%d ",ans[read()]);} 37 }