Non-overlapping Intervals

Problem

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

## Solution
Counting Unique Paths Solution
```java
/**
 * Definition for an interval.
 * public class Interval {
 *     int start;
 *     int end;
 *     Interval() { start = 0; end = 0; }
 *     Interval(int s, int e) { start = s; end = e; }
 * }
 */
public class Solution {
    public int eraseOverlapIntervals(Interval[] intervals) {
        if (intervals == null || intervals.length < 2) return 0;
        Arrays.sort(intervals, (a, b) -> a.end - b.end);
        int count = 1, end = intervals[0].end;
        for (Interval interval : intervals) {
            if (interval.start >= end) {
                count++;
                end = interval.end;
            }
        }
        return intervals.length - count;
    }
}

Analysis

This problem is actually equal to finding the unique intervals
As long as we know the unique intervals count, we return intervals.length - count