49 lines
1.3 KiB
C++
49 lines
1.3 KiB
C++
#include <vector>
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#include <unordered_map>
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#include <iostream>
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int main() {
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std::vector<int> alreadyDiscovered;
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std::unordered_map<int, int> divsumMap;
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int count = 0;
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for (int N = 1; N <= 20000; ++N)
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{
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int divSumN = 0;
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for (int i = 1; i <= N / 2; ++i)
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{
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if (fmod(N, i) == 0)
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{
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divSumN += i;
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}
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}
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// populate map of integers to the sum of their proper divisors
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if (divSumN != 1) // do not include primes
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divsumMap[N] = divSumN;
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for (std::unordered_map<int, int>::iterator it = divsumMap.begin(); it != divsumMap.end(); ++it)
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{
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int M = it->first;
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int divSumM = it->second;
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int divSumN = divsumMap[N];
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if (N != M && divSumM == N && divSumN == M)
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{
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// do not print duplicate pairs
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if (std::find(alreadyDiscovered.begin(), alreadyDiscovered.end(), N) != alreadyDiscovered.end())
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break;
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std::cout << "[" << M << ", " << N << "]" << std::endl;
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alreadyDiscovered.push_back(M);
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alreadyDiscovered.push_back(N);
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count++;
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}
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}
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}
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std::cout << count << " amicable pairs discovered" << std::endl;
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}
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