Project Euler：Problem 21 Amicable numbers

标签：c++   project euler   

Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
If d(a) = b and d(b) = a, where a ≠ b, then a and b are an amicable pair and each of a and b are called amicable numbers.

For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.

Evaluate the sum of all the amicable numbers under 10000.

求满足这个要求的数的和

#include <iostream>
#include<map>
using namespace std;

int count(int a)
{
	int res = 0;
	for (int i = 1; i < a; i++)
	{
		if (a%i == 0)
			res += i;
	}
	return res;
}


int main()
{
	map<int, int>mp;
	for (int i = 1; i < 10000; i++)
	{
		mp[i] = count(i);
	}
	int res = 0;
	for (int i = 1; i < 10000; i++)
	{
		if (mp[i] != i&&mp[i] < 10000 && mp[mp[i]] == i)
		{
			//cout << i << " " << mp[i] << endl;
			res+=i;
		}
	}
	cout << res << endl;
	system("pause");
	return 0;
}

Project Euler：Problem 21 Amicable numbers

标签：c++   project euler   

原文地址：http://blog.csdn.net/youb11/article/details/46311467