Java:将 int[] 转换为范围的最小表示

Question

给定一组 int 值，如何将序列解析为计数序列符号？

例子:

{1, 2, 3, 4, 5, 9, 13, 14, 15} -> "1-5,9,13-15"
{4, 6, 8, 10, 11, 12, 15, 17}  -> "4,6,8,10-12,15,17"

我正在寻找一种可以产生这些结果的方法。这是我到目前为止所拥有的，但在这一点上我非常难过:

测试代码:

import java.util.Arrays;
public class TestSequencing {
    public static void main(String[] args) {
        int[] numbers1 = {1, 2, 3, 4, 5, 9, 13, 14, 15};
        String numbers1s = "1-5,9,13-15";
        System.out.println(Arrays.toString(numbers1));
        System.out.println("Expected:\t" + numbers1s);
        System.out.println("Produced:\t" + sequenceNums(numbers1) + "\n");

        int[] numbers2 = {3, 5, 6, 9, 12};
        String numbers2s = "3,5-6,9,12";
        System.out.println(Arrays.toString(numbers2));
        System.out.println("Expected:\t" + numbers2s);
        System.out.println("Produced:\t" + sequenceNums(numbers2) + "\n");

        int[] numbers3 = {1, 2, 3, 4, 5, 6, 7};
        String numbers3s = "1-7";
        System.out.println(Arrays.toString(numbers3));
        System.out.println("Expected:\t" + numbers3s);
        System.out.println("Produced:\t" + sequenceNums(numbers3) + "\n");
    }

    public static String sequenceNums(int[] nums) {
        StringBuilder sb = new StringBuilder();
        int rangeStart = nums[0];
        int previous = nums[0];
        int current;
        int expected = previous + 1;

        for (int i = 1 ; i < nums.length ; i++) {
            current = nums[i];
            expected = previous + 1;               
            if (current != expected || i == (nums.length - 1)) {
                if (current == rangeStart) {
                    sb.append(previous + ",");
                } else {
                    sb.append(rangeStart + "-" + previous + ",");
                }                
                rangeStart = current;
            }              
            previous = current;
        }
        if (sb.charAt(sb.length() - 1) == ',') {
            sb.deleteCharAt(sb.length() - 1);
        }
        return sb.toString();
    }
}

输出:

[1, 2, 3, 4, 5, 9, 13, 14, 15]
Expected:   1-5,9,13-15
Produced:   1-5,9-9,13-14

[3, 5, 6, 9, 12]
Expected:   3,5-6,9,12
Produced:   3-3,5-6,9-9

[1, 2, 3, 4, 5, 6, 7]
Expected:   1-7
Produced:   1-6

Answer 1

试试这个:

private static void appendRange(StringBuilder sb, int begin, int end) {
    sb.append(",").append(begin);
    if (end != begin)
        sb.append("-").append(end);
}

public static String sequenceNums(int[] nums) {
    StringBuilder sb = new StringBuilder();
    if (nums.length == 0) return sb.toString();
    int begin = nums[0], end = nums[0];
    for (int cur : nums)
        if (cur - end <= 1)
            end = cur;
        else {
            appendRange(sb, begin, end);
            begin = end = cur;
        }
    appendRange(sb, begin, end);
    return sb.substring(1);
}

@Test
public void testSequenceNums() {
    assertEquals("1-5,9,13-15", sequenceNums(new int[] {1, 2, 3, 4, 5, 9, 13, 14, 15}));
    assertEquals("4,6,8,10-12,15,17", sequenceNums(new int[] {4, 6, 8, 10, 11, 12, 15, 17}));
    assertEquals("1-7", sequenceNums(new int[] {1, 2, 3, 4, 5, 6, 7}));
    assertEquals("", sequenceNums(new int[] {}));
}