Formatted question description: https://leetcode.ca/all/1893.html

1893. Check if All the Integers in a Range Are Covered

Level

Easy

Description

You are given a 2D integer array ranges and two integers left and right. Each ranges[i] = [start_i, end_i] represents an inclusive interval between start_i and end_i.

Return true if each integer in the inclusive range [left, right] is covered by at least one interval in ranges. Return false otherwise.

An integer x is covered by an interval ranges[i] = [start_i, end_i] if start_i <= x <= end_i.

Example 1:

Input: ranges = [[1,2],[3,4],[5,6]], left = 2, right = 5

Output: true

Explanation: Every integer between 2 and 5 is covered:

  • 2 is covered by the first range.
  • 3 and 4 are covered by the second range.
  • 5 is covered by the third range.

Example 2:

Input: ranges = [[1,10],[10,20]], left = 21, right = 21

Output: false

Explanation: 21 is not covered by any range.

Constraints:

  • 1 <= ranges.length <= 50
  • 1 <= start_i <= end_i <= 50
  • 1 <= left <= right <= 50

Solution

Since the data range is limited, for each range in ranges, consider the intersection of range and [left, right], and add all the numbers in the intersection into a hash set. Finally, check whether the hash set’s size is right - left + 1.

class Solution {
    public boolean isCovered(int[][] ranges, int left, int right) {
        Set<Integer> set = new HashSet<Integer>();
        for (int[] range : ranges) {
            int start = Math.max(range[0], left);
            int end = Math.min(range[1], right);
            for (int i = start; i <= end; i++)
                set.add(i);
        }
        return set.size() == right - left + 1;
    }
}

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