435. Non-overlapping Intervals (Medium)-不重叠的区间个数

不重叠的区间个数

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.
Input: [ [1,2], [2,3] ]

Output: 0

Explanation: You don't need to remove any of the intervals since they're already non-overlapping.
题目描述：计算让一组区间不重叠所需要移除的区间个数。

先计算最多能组成的不重叠区间个数，然后用区间总个数减去不重叠区间的个数。

在每次选择中，区间的结尾最为重要，选择的区间结尾越小，留给后面的区间的空间越大，那么后面能够选择的区间个数也就越大。

按区间的结尾进行排序，每次选择结尾最小，并且和前一个区间不重叠的区间。

public int eraseOverlapIntervals(Interval[] intervals) {
    if (intervals.length == 0) {
        return 0;
    }
    Arrays.sort(intervals, Comparator.comparingInt(o -> o.end));
    int cnt = 1;
    int end = intervals[0].end;
    for (int i = 1; i < intervals.length; i++) {
        if (intervals[i].start < end) {
            continue;
        }
        end = intervals[i].end;
        cnt++;
    }
    return intervals.length - cnt;
}