leetcode324 Wiggle Sort II

"""
Given an unsorted array nums, reorder it such that nums[0] < nums[1] > nums[2] < nums[3]....
Example 1:
Input: nums = [1, 5, 1, 1, 6, 4]
Output: One possible answer is [1, 4, 1, 5, 1, 6].
Example 2:
Input: nums = [1, 3, 2, 2, 3, 1]
Output: One possible answer is [2, 3, 1, 3, 1, 2].
"""
"""
先排序，再折半拆成两个子数组，再归并
但本题的关键是需要对两个子数组由后向前取元素
"""
class Solution:
    def wiggleSort(self, nums):
        """
        Do not return anything, modify nums in-place instead.
        """
        l = sorted(nums)
        mid = (len(l)+1)//2
        l1 = l[:mid]
        l2 = l[mid:]
        k, i, j = 0, len(l1)-1, len(l2)-1 #!!!逆着合并 测试[4, 5, 5, 6]
        while i >= 0 or j >= 0: #bug 写成了i>0
            if i >= 0:
                nums[k] = l1[i]
                i -= 1
                k += 1
            if j >= 0:
                nums[k] = l2[j]
                j -= 1
                k += 1
if __name__ == '__main__':
    nums = [1,3,2,2,3,1]
    ans = Solution()
    res = ans.wiggleSort(nums)