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.
Example1:
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.
Example2:
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.
Example3:
Input: [ [1,2], [2,3] ]
Output: 0
Explanation: You don't need to remove any of the intervals since they're already non-overlapping.
先对区间进行排序,然后遍历所有区间,尽量去掉长区间,则保留的区间数目一定最多。
bool cmp(Interval a, Interval b) {
return a.start < b.start;
}
class Solution {
public:
int eraseOverlapIntervals(vector & intervals) {
sort(intervals.begin(), intervals.end(), cmp);
int res = 0, pre = 0; //res记录保留区间的个数,pre记录每次需要判断是否重叠的起始区间
for (int i = 1; i < intervals.size(); i++) {
if (intervals[i].start < intervals[pre].end) {
res++; //当前区间起始值小于pre区间的末尾保留上一个区间
if (intervals[i].end < intervals[pre].end) pre = i;
//这个的意思是从集合中去掉的元素是pre(因为pre太长)
}
else pre = i; //区间i和区间pre已经不重叠,需要判断重叠的起始区间pre后移
}
return res;
}
};