Submission #2197993

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Source Code Expand

#include <stdio.h>
#include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
#include <array>
#include <iomanip>
using namespace std;
#ifdef DEBUG
#define D(x) x
#else
#define D(x) x
#endif

#define FOR(i, a, b) for(int i = (a); i < (b); ++i)
#define REP(i, n) for(int i = 0; i < (n); ++i)


int main(){
	cout << setprecision(10);

	int n; cin >> n;
	vector<int> c;
	REP(i,n){
		int cc; cin >> cc;
		c.push_back(cc);
	}
	sort(c.begin(), c.end() );
	array< int, 101 > div_cnt = {0}; // < num, count > 

	vector<int> divider_count;
	REP( i, c.size() ){
		FOR( j, i+1, c.size() ){
			if( c[j] % c[i]  == 0 ){
				div_cnt[j] += 1;
			}
			if( c[j] == c[i] ) div_cnt[i] += 1;
		}
	}

	// print
	double ret = 0;
	REP( i , c.size() ){
		int div = div_cnt[i];
		ret += (double)( ( div + 2 ) / 2 ) / ( div + 1.0 );
	}
	cout << ret << endl;
}

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