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  • 【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:

    1. You may assume the interval's end point is always bigger than its start point.
    2. 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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  • 原文地址:https://www.cnblogs.com/seyjs/p/10494587.html
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