240217 시소 짝꿍

public long solution(int[] weights) {
	long answer = 0;
	Map<Integer, Integer> weightMap = new HashMap<>();

	for (int weight : weights) {
		weightMap.put(weight, weightMap.getOrDefault(weight, 0) + 1);
	}

	Integer[] uniqueWeights = weightMap.keySet().toArray(new Integer[0]);
	Integer[] weightCounts = weightMap.values().toArray(new Integer[0]);

	for (int i = 0; i < uniqueWeights.length - 1; i++) {
		int count = weightCounts[i];
		if (count > 1) {
			answer += (long) count * (count - 1) / 2;
		}
		for (int j = i + 1; j < uniqueWeights.length; j++) {
			int weight1 = uniqueWeights[i];
			int weight2 = uniqueWeights[j];

			if (isPartner(weight1, weight2)) {
				answer += (long) count * weightCounts[j];
			}
		}
	}
	int lastCount = weightCounts[uniqueWeights.length - 1];
	if (lastCount > 1) {
		answer += (long) lastCount * (lastCount - 1) / 2;
	}

	return answer;
}

private boolean isPartner(int f1, int f2) {
	int[] factors = { 2, 3, 4 };
	for (int factor1 : factors) {
		for (int factor2 : factors) {
			if (f1 * factor1 == f2 * factor2) {
				return true;
			}
		}
	}
	return false;
}

출처:https://school.programmers.co.kr/learn/courses/30/lessons/152996