[프로그래머스] 우박수열 정적분

문제

https://school.programmers.co.kr/learn/courses/30/lessons/134239

프로그래머스

접근 방법 및 풀이

문제 설명에 따라 우박수열을 구한 후 ranges 배열의 내용 대로 면적을 구함

import java.util.ArrayList;
import java.util.List;

public class Q30_134239 {
    public double[] solution(int k, int[][] ranges) {
        List<Integer> collatzList = this.getCollatzNumbers(k);
        double[] integrals = this.getIntegrals(collatzList);
        double[] answer = new double[ranges.length];

        int collatzLength = collatzList.size();
        for (int i = 0; i < ranges.length; i++) {
            int[] range = ranges[i];
            answer[i] = getIntegral(integrals, range[0], collatzLength + range[1] - 1);
        }

        return answer;
    }

    public double getIntegral(double[] integrals, int start, int end) {
        if (start == end) {
            return 0.0;
        } else if (start > end) {
            return -1.0;
        }

        double total = 0;
        for (int i = start + 1; i <= end; i++) {
            total += integrals[i];
        }
        return total;
    }

    public List<Integer> getCollatzNumbers(int number) {
        List<Integer> list = new ArrayList<>();
        while (true) {
            list.add(number);
            if (number == 1) {
                break;
            }
            if (number % 2 == 0) {
                number = number / 2;
            } else {
                number = number * 3 + 1;
            }
        }
        return list;
    }

    public double[] getIntegrals(List<Integer> collatzList) {
        int length = collatzList.size();
        double[] results = new double[length];
        results[0] = 0.0;

        for (int i = 1; i < length; i++) {
            int x0 = collatzList.get(i - 1);
            int x1 = collatzList.get(i);
            results[i] = (double) (x0 + x1) / 2.0;
        }

        return results;
    }
}