缺失的区间

/*
 * Problem: Missing Ranges (LeetCode 163)
 * Given a sorted integer array nums, where the range of elements are in the inclusive range [lower, upper], return its missing ranges.
 * Example:
 * Input: nums = [0, 1, 3, 50, 75], lower = 0, upper = 99
 * Output: ["2", "4->49", "51->74", "76->99"]
 * 
 * Approach (Using Java Streams):
 * 1. Convert the nums array to a list and add lower-1 and upper+1 to handle the boundaries.
 * 2. Use IntStream.range to iterate through the list and find gaps between consecutive numbers.
 * 3. Collect the missing ranges into a result list.
 */
 
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
 
public class MissingRangesStream {
    public List<String> findMissingRanges(int[] nums, int lower, int upper) {
        List<Integer> list = new ArrayList<>();
        list.add(lower - 1);
        list.addAll(Arrays.stream(nums).boxed().collect(Collectors.toList()));
        list.add(upper + 1);
 
        return IntStream.range(0, list.size() - 1)
                .mapToObj(i -> formatRange(list.get(i) + 1, list.get(i + 1) - 1))
                .filter(range -> !range.isEmpty())
                .collect(Collectors.toList());
    }
 
    private String formatRange(int start, int end) {
        return (start <= end) ? (start == end ? String.valueOf(start) : start + "->" + end) : "";
    }
 
    public static void main(String[] args) {
        MissingRangesStream mrs = new MissingRangesStream();
        int[] nums = {0, 1, 3, 50, 75};
        int lower = 0;
        int upper = 99;
        System.out.println(mrs.findMissingRanges(nums, lower, upper));
    }
}