163 Missing Ranges

163. Missing Ranges

1. Question

Given a sorted integer array where the range of elements are in the inclusive range [lower,upper], return its missing ranges.

For example, given[0, 1, 3, 50, 75],lower= 0 andupper= 99, return["2", "4->49", "51->74", "76->99"].

2. Implementation

(1) Scan Line

class Solution {
    public List<String> findMissingRanges(int[] nums, int lower, int upper) {
        List<String> res = new ArrayList<>();

        for (int i = 0; i <= nums.length; i++) {
            long start = i == 0 ? lower : (long)nums[i - 1] + 1;
            long end = i == nums.length ? upper : (long)nums[i] - 1;
            addMissingRange(res, start, end);
        }
        return res;
    }

    public void addMissingRange(List<String> res, long start, long end) {
        if (start > end) {
            return;
        }

        if (start == end) {
            res.add(start + "");
        }
        else {
            res.add(start + "->" + end);
        }
    }
}

3. Time & Space Complexity

Scan Line: 时间复杂度O(n), 空间复杂度O(n)