无重叠区间

class :
    def eraseOverlapIntervals(self, intervals):
        """
        :type intervals: List[Interval]
        :rtype: int
        """
        n = len(intervals)
        if n <= 1:
            return n
        intervals = sorted(intervals, key=lambda x:(x[1],-x[0]))
        res = 0 
        prv = 0
        for i in range(n-1):
            if intervals[i+1][0] < intervals[prv][1]:
                res += 1
            else:
                prv = i+1
        return res