Leetcode435 Non-overlapping Intervals

Description

Given a collection of intervals, find the minimum number of intervals you need to remove to make the rest of the intervals non-overlapping.

Example

Example 1:

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

Example 2:

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

Example 3:

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

Note:

• You may assume the interval’s end point is always bigger than its start point.
• Intervals like [1,2] and [2,3] have borders “touching” but they don’t overlap each other.

Solution

Minimum number of intervals you need to remove == find the maximum number of intervals that are non-overlapping

• Time Complexity: $O(Nlog^N)$
• Space Complexity: $O(1)$

class Solution {
    public int eraseOverlapIntervals(int[][] intervals) {
        if (intervals.length == 0) return 0;
        Arrays.sort(intervals, (a, b)->a[1] - b[1]);
        
        int end = intervals[0][1];
        int max = 1;
        for (int i = 1; i < intervals.length; i++){
            if (intervals[i][0] >= end){
                max++;
                end = intervals[i][1];
            }
        }
        
        return intervals.length - max;
    }
}

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