non-overlapping-intervals.py

# Time:  O(nlogn)
# Space: O(1)

# 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.

# 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
        """
        intervals.sort(key=lambda interval: interval.start)
        result, prev = 0, 0
        for i in xrange(1, len(intervals)):
            if intervals[i].start < intervals[prev].end:
                if intervals[i].end < intervals[prev].end:
                    prev = i
                result += 1
            else:
                prev = i
        return result