LeetCode 1893. Check if All the Integers in a Range Are Covered Solution in Java, C++, Python & More | Explanation + Code

Description

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

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] = [starti, endi] if starti <= x <= endi.

 

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 <= starti <= endi <= 50
• 1 <= left <= right <= 50

Solutions

Solution 1: Difference Array

We can use the idea of a difference array to create a difference array diff of length 52.

Next, we iterate through the array ranges. For each interval [l, r], we increment diff[l] by 1 and decrement diff[r + 1] by 1.

Then, we iterate through the difference array diff, maintaining a prefix sum s. For each position i, we increment s by diff[i]. If s \le 0 and left \le i \le right, it indicates that an integer i within the interval [left, right] is not covered, and we return false.

If we finish iterating through the difference array diff without returning false, it means that every integer within the interval [left, right] is covered by at least one interval in ranges, and we return true.

The time complexity is O(n + M), and the space complexity is O(M). Here, n is the length of the array ranges, and M is the maximum value of the interval, which in this case is M \le 50.

PythonJavaC++GoTypeScriptJavaScript

class Solution: def isCovered(self, ranges: List[List[int]], left: int, right: int) -> bool: diff = [0] * 52 for l, r in ranges: diff[l] += 1 diff[r + 1] -= 1 s = 0 for i, x in enumerate(diff): s += x if s <= 0 and left <= i <= right: return False return True(code-box)

class Solution { public boolean isCovered(int[][] ranges, int left, int right) { int[] diff = new int[52]; for (int[] range : ranges) { int l = range[0], r = range[1]; ++diff[l]; --diff[r + 1]; } int s = 0; for (int i = 0; i < diff.length; ++i) { s += diff[i]; if (s <= 0 && left <= i && i <= right) { return false; } } return true; } }(code-box)

class Solution { public: bool isCovered(vector<vector<int>>& ranges, int left, int right) { vector<int> diff(52); for (auto& range : ranges) { int l = range[0], r = range[1]; ++diff[l]; --diff[r + 1]; } int s = 0; for (int i = 0; i < diff.size(); ++i) { s += diff[i]; if (s <= 0 && left <= i && i <= right) { return false; } } return true; } };(code-box)

func isCovered(ranges [][]int, left int, right int) bool { diff := [52]int{} for _, e := range ranges { l, r := e[0], e[1] diff[l]++ diff[r+1]-- } s := 0 for i, x := range diff { s += x if s <= 0 && left <= i && i <= right { return false } } return true }(code-box)

function isCovered(ranges: number[][], left: number, right: number): boolean { const diff: number[] = Array(52).fill(0); for (const [l, r] of ranges) { ++diff[l]; --diff[r + 1]; } let s = 0; for (let i = 0; i < diff.length; ++i) { s += diff[i]; if (s <= 0 && left <= i && i <= right) { return false; } } return true; }(code-box)

/** * @param {number[][]} ranges * @param {number} left * @param {number} right * @return {boolean} */ var isCovered = function (ranges, left, right) { const diff = Array(52).fill(0); for (const [l, r] of ranges) { ++diff[l]; --diff[r + 1]; } let s = 0; for (let i = 0; i < diff.length; ++i) { s += diff[i]; if (s <= 0 && left <= i && i <= right) { return false; } } return true; };(code-box)