题目描述:
归并排序
使用排序算法将数组内容进行排序,时间复杂度要低于O(n^2)
示例 1:
输入: nums = [2, 4, 2, 6, 7, 0, 1]
输出: nums = [0, 1, 2, 2, 4, 6, 7]
算法实现:
解题思路
归并算法类似于两个有序数组合并成一个新的有序数组的算法,
1、利用递归将数组分为两半,然后再对半分,直到分成单个数据
2、将两个分开的有序数据利用归并算法合并成一个新的数组。
# 除以2 取上界的技巧,可以使用右移mid = (left + right)>>1
def mergeSort(nums, left, right, new_nums):
if left < right:
mid = (left + right)>>1
mergeSort(nums, left, mid, new_nums)
mergeSort(nums, mid + 1, right, new_nums)
merge(nums, mid, left, right, new_nums)
def merge(nums, mid, left, right, new_nums):
"""
将两个数组合并成一个数组
:return:
"""
i,j,k=left,mid+1,left
while i <= mid and j <= right:
if nums[i] < nums[j]:
new_nums[k] = nums[i]
i += 1
else:
new_nums[k] = nums[j]
j+=1
k += 1
while i <= mid:
new_nums[k] = nums[i]
i += 1
k += 1
while j <= right:
new_nums[k] = nums[j]
j += 1
k += 1
for n in range(k-left):
nums[left+n] = new_nums[left + n]