programmers_시소 짝꿍_java

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

프로그래머스

import java.util.*;

class Solution {
    public long solution(int[] weights) {
        long answer = 0;

        Arrays.sort(weights);
        Map<Double, Integer> map = new HashMap<>();
        for (int weight : weights){
            answer += isPair(weight, map);
        }

        return answer;
    }

    public int isPair(int weight, Map<Double, Integer> map){
        int res = 0;

        // 자신 보다 작거나 같은 페어의 경우의 수 4가지
        double case1 = weight * 1.0;
        double case2 = (weight * 1.0 )/ 2.0;
        double case3 = (weight * 2.0 )/ 3.0;
        double case4 = (weight * 3.0 )/ 4.0;

        if (map.containsKey(case1)){
            res += map.get(case1);
        }
        if (map.containsKey(case2)){
            res += map.get(case2);
        }
        if (map.containsKey(case3)){
            res += map.get(case3);
        }
        if (map.containsKey(case4)){
            res += map.get(case4);
        }
        map.put(case1, map.getOrDefault(case1, 0) + 1);

        return res;
    }
}