1288

1288. Remove Covered Intervals (Medium)

Given an array intervals where intervals[i] = [li, ri] represent the interval [li, ri), remove all intervals that are covered by another interval in the list.

The interval [a, b) is covered by the interval [c, d) if and only if c <= a and b <= d.

Return the number of remaining intervals.

 

Example 1:

Input: intervals = [[1,4],[3,6],[2,8]]
Output: 2
Explanation: Interval [3,6] is covered by [2,8], therefore it is removed.

Example 2:

Input: intervals = [[1,4],[2,3]]
Output: 1

 

Constraints:

• 1 <= intervals.length <= 1000
• intervals[i].length == 2
• 0 <= li <= ri <= 105
• All the given intervals are unique.

Companies:
Facebook, Amazon

Related Topics:
Array, Sorting

Solution 1. Sorting + Greedy

// OJ: https://leetcode.com/problems/remove-covered-intervals/
// Author: github.com/lzl124631x
// Time: O(NlogN)
// Space: O(1)
class Solution {
public:
    int removeCoveredIntervals(vector<vector<int>>& A) {
        sort(begin(A), end(A), [](auto &a, auto &b) { return a[0] != b[0] ? a[0] < b[0] : a[1] > b[1]; });
        int ans = A.size(), e = INT_MIN;
        for (auto &r : A) {
            if (r[1] <= e) --ans;
            else e = r[1];
        }
        return ans;
    }
};