435. Non-overlapping Intervals

Problem Link

Description

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Given an array of intervals intervals where intervals[i] = [starti, endi], return the minimum number of intervals you need to remove to make the rest of the intervals non-overlapping.

Note that intervals which only touch at a point are non-overlapping. For example, [1, 2] and [2, 3] are non-overlapping.

 

Example 1:

Input: intervals = [[1,2],[2,3],[3,4],[1,3]]
Output: 1
Explanation: [1,3] can be removed and the rest of the intervals are non-overlapping.

Example 2:

Input: intervals = [[1,2],[1,2],[1,2]]
Output: 2
Explanation: You need to remove two [1,2] to make the rest of the intervals non-overlapping.

Example 3:

Input: intervals = [[1,2],[2,3]]
Output: 0
Explanation: You don't need to remove any of the intervals since they're already non-overlapping.

 

Constraints:

• 1 <= intervals.length <= 105
• intervals[i].length == 2
• -5 * 104 <= starti < endi <= 5 * 104

Solution

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Python3

class Solution:
    def eraseOverlapIntervals(self, intervals: List[List[int]]) -> int:
        N = len(intervals)
 
        if N < 2: return 0
 
        intervals.sort()
        last = intervals[0][1]
        res = 0
 
        for i in range(1, N):
            if intervals[i][0] < last:
                res += 1
                last = min(last, intervals[i][1])
            else:
                last = intervals[i][1]
 
        return res