hiho一下 第八十九周 Divisors

描述

Given an integer n, for all integers not larger than n, find the integer with the most divisors. If there is more than one integer with the same number of divisors, print the minimum one.

输入

One line with an integer n.

For 30% of the data, n ≤ 103

For 100% of the data, n ≤ 1016

输出

One line with an integer that is the answer.

题目分析

#include<stdio.h>
#include<math.h>

int prime[13] = {2,3,5,7,11,13,17,19,23,29,31,37,41};
long long N, max = 1, ans = 1;

void DFS(long long now, long long divisor, int prime_index, long long pre){
if(max < divisor || (max == divisor && now < ans)){
max = divisor;
ans = now;
}
if(prime_index > 12) return;
long long i = 1, newnow;
while(i <= pre && now*pow(prime[prime_index], i) <= N){
newnow = now*pow(prime[prime_index], i);
DFS(newnow, divisor*(i+1), prime_index+1, i);
i++;
}
}

int main(){
scanf("%lld", &N);
DFS(1, 1, 0, log2(N));
printf("%lld\n", ans);
return 0;
}