【leetcode】435. Non-overlapping Intervals
题目如下:
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.
解题思路:本题可以用贪心算法。 首先对 intervals 按start从小到大排序,如果start相同,则按end从小到大。接下来遍历intervals,如果intervals相邻的两个元素有重叠,删除掉end较大的那个,最后intervals中留下来的元素都是不重叠的。
代码如下:
# Definition for an interval.
# class Interval(object):
# def __init__(self, s=0, e=0):
# self.start = s
# self.end = e class Solution(object):
def eraseOverlapIntervals(self, intervals):
"""
:type intervals: List[Interval]
:rtype: int
"""
def cmpf(i1,i2):
if i1.start != i2.start:
return i1.start - i2.start
return i1.end - i2.end
intervals.sort(cmp=cmpf)
keep = None
res = 0
while len(intervals) > 0:
item = intervals.pop(0)
if keep == None or keep.end <= item.start:
keep = item
elif keep.end <= item.end:
res += 1
elif keep.end > item.end:
keep = item
res += 1
return res
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