56. Merge Intervals

Given a collection of intervals, merge all overlapping intervals.

Example 1:
Input: [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].

Example 2:
Input: [[1,4],[4,5]]
Output: [[1,5]]
Explanation: Intervals [1,4] and [4,5] are considered overlapping.

解题思路：
题意很明确，首先对各区间按开始来排序（选用了快速排序），最后遍历，如果前面和后面的区间有重合（分三种情况讨论），合并。

class Solution(object):
    def merge(self, intervals):
        """
        :type intervals: List[List[int]]
        :rtype: List[List[int]]
        """
        # index = 0
        self.quicksort(intervals, 0,len(intervals)-1)
        result = []
        # print(intervals)
        for i in range(len(intervals)):
            if i < len(intervals)-1 and intervals[i][1] >= intervals[i+1][0] and intervals[i][1] <= intervals[i+1][1]:
                # print(intervals[i+1][0],intervals[i][0])
                intervals[i+1][0] = intervals[i][0]
                # index += 1
            elif i < len(intervals)-1 and intervals[i][1] >= intervals[i+1][0] and intervals[i][1] > intervals[i+1][1]:
                intervals[i+1][0] = intervals[i][0]
                intervals[i+1][1] = intervals[i][1]
                # index += 1
            else:
                result.append(intervals[i])
        # print(intervals)
        return result

    def quicksort(self,nums,l,h):
        if l < h:
            pivotpos = self.partition(nums,l,h)
            self.quicksort(nums,l,pivotpos - 1)
            self.quicksort(nums,pivotpos + 1,h)

    def partition(self,nums,l,h):
        p = nums[l]
        while l < h:
            while l < h and nums[h][0] >= p[0]:
                h -= 1
            nums[l] = nums[h]
            while l < h and nums[l][0] <= p[0]:
                l += 1
            nums[h] = nums[l]
        nums[l] = p
        return l