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1288. Remove Covered Intervals

Description

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.

Solutions

• Sort intervals by increasing of startTime and decreasing of endTime.
• cnt = 1: cnt is the result.
• pre = intervals[0]: pre is the last interval
• For each interval in intervals
  • if pre.endTime < interval.endTime, means interval is not overlapped then we count cnt, and update pre = interval
  • else we do nothing
• Return cnt

• Java
• C++
• Python
• Go

• class Solution {
      public int removeCoveredIntervals(int[][] intervals) {
          Arrays.sort(intervals, (a, b) -> a[0] - b[0] == 0 ? b[1] - a[1] : a[0] - b[0]);
          int[] pre = intervals[0];
          int cnt = 1;
          for (int i = 1; i < intervals.length; ++i) {
              if (pre[1] < intervals[i][1]) {
                  ++cnt;
                  pre = intervals[i];
              }
          }
          return cnt;
      }
  }
  

• class Solution {
  public:
      int removeCoveredIntervals(vector<vector<int>>& intervals) {
          sort(intervals.begin(), intervals.end(), [](const vector<int>& a, const vector<int>& b) { return a[0] == b[0] ? b[1] < a[1] : a[0] < b[0]; });
          int cnt = 1;
          vector<int> pre = intervals[0];
          for (int i = 1; i < intervals.size(); ++i) {
              if (pre[1] < intervals[i][1]) {
                  ++cnt;
                  pre = intervals[i];
              }
          }
          return cnt;
      }
  };
  

• class Solution:
      def removeCoveredIntervals(self, intervals: List[List[int]]) -> int:
          intervals.sort(key=lambda x: (x[0], -x[1]))
          cnt, pre = 1, intervals[0]
          for e in intervals[1:]:
              if pre[1] < e[1]:
                  cnt += 1
                  pre = e
          return cnt
  
  

• func removeCoveredIntervals(intervals [][]int) int {
  	sort.Slice(intervals, func(i, j int) bool {
  		if intervals[i][0] == intervals[j][0] {
  			return intervals[j][1] < intervals[i][1]
  		}
  		return intervals[i][0] < intervals[j][0]
  	})
  	cnt := 1
  	pre := intervals[0]
  	for i := 1; i < len(intervals); i++ {
  		if pre[1] < intervals[i][1] {
  			cnt++
  			pre = intervals[i]
  		}
  	}
  	return cnt
  }
  

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