programmers_우박수열 정적분_java

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

프로그래머스

import java.util.*;

class Solution {
    public double[] solution(int k, int[][] ranges) {
        double[] answer = new double[ranges.length];

        int[] graph = collatz(k);
        int graphtSize = graph.length;

        double[] area = calArea(graph);

        int answerIdx = 0;
        for (int[] r : ranges){
            int[] range = calRange(r, graphtSize-1);
            if (range[0] > range[1]){
                answer[answerIdx] = -1.0;
            }else{
                answer[answerIdx] = area[range[1]] - area[range[0]];
            }
            answerIdx++;
        }

        return answer;
    }
    
  // 콜라츠 추측
    public int[] collatz(int k){
        List<Integer> list = new ArrayList<>();
        list.add(k);
        while(k > 1){
            if (k % 2 == 0){
                k = k/2;
            }else {
                k = k*3 + 1;
            }
            list.add(k);
        }
        return listTointArray(list);
    }
    
    // List -> Array
    public int[] listTointArray(List<Integer> list){
        int[] arr = new int[list.size()];
        int idx = 0;
        for (int i : list){
            arr[idx++] = i; // y좌표
        }
        return arr;
    }
    
// 각 점까지의 영역 합 구하기
    public static double[] calArea(int[] graph){
        int graphLength = graph.length;
        double[] area = new double[graphLength];

        int beforeY = graph[0];

        for (int i = 1; i<graphLength; i++){
            int big = Math.max(beforeY, graph[i]);
            int small = Math.min(beforeY, graph[i]);

            // 사각형 영역
            area[i] += small;
            // 삼각형 영역
            if (big!=small){ // 같은 값인경우 = 사각형
                area[i] += 0.5 * 1 * (big-small);
            }

            area[i] += area[i-1];
            beforeY = graph[i];
        }

        return area;
    }

 // 정적분 범위 계산
    public int[] calRange(int[] range, int lastIdx){
        int[] r = new int[2];

        r[0] = range[0];
        r[1] = lastIdx + range[1];

        return r;
    }
}