230412 시소 짝꿍

public 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;
}

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

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