Range.java

package kyu4;

/**
 *  4 kyu - Range Extraction
 *
 *  https://www.codewars.com/kata/51ba717bb08c1cd60f00002f/java
 *
 *  DESCRIPTION:
 * A format for expressing an ordered list of integers is to use a comma separated list of either
 *
 * individual integers
 * or a range of integers denoted by the starting integer separated from the end integer in the range by a dash, '-'.
 * The range includes all integers in the interval including both endpoints. It is not considered a range unless it spans at least 3 numbers. For example "12,13,15-17"
 * Complete the solution so that it takes a list of integers in increasing order and returns a correctly formatted string in the range format.
 *
 * Example:
 *
 * Solution.rangeExtraction(new int[] {-10, -9, -8, -6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20})
 * # returns "-10--8,-6,-3-1,3-5,7-11,14,15,17-20"
 *
 *
 */

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

public class Range {
    public static String rangeExtraction(int[] arr) {
        List<String> list = new ArrayList<>();
        int count = 0;
        for (int i = 0; i < arr.length; ) {
            count = 0;
            String start = String.valueOf(arr[i]);
            while (i != arr.length - 1 && arr[i + 1] - arr[i] == 1) {
                count++;
                i++;
            }
            if (count > 0) {
                if (count > 1) {
                    start += "-" + (Integer.parseInt(start) + count);
                } else {
                    i--;
                }
            }
            list.add(start);
            i++;
        }
        return String.join(",", list);
    }
}