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Re-implement merge sort function. (#888)

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Yudong Jin
2023-10-26 02:56:33 +08:00
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parent 7822bf9cd4
commit e441ee4e35
8 changed files with 186 additions and 181 deletions
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codes/python/chapter_sorting/merge_sort.py
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@ -1,39 +1,38 @@
"""
File: merge_sort.py
Created Time: 2022-11-25
Author: timi (xisunyy@163.com)
Author: timi (xisunyy@163.com), Krahets (krahets@163.com)
"""
def merge(nums: list[int], left: int, mid: int, right: int):
"""合并左子数组和右子数组"""
# 左子数组区间 [left, mid]
# 右子数组区间 [mid + 1, right]
# 初始化辅助数组
tmp = list(nums[left : right + 1])
# 左子数组的起始索引和结束索引
left_start = 0
left_end = mid - left
# 右子数组的起始索引和结束索引
right_start = mid + 1 - left
right_end = right - left
# i, j 分别指向左子数组、右子数组的首元素
i = left_start
j = right_start
# 通过覆盖原数组 nums 来合并左子数组和右子数组
for k in range(left, right + 1):
# 若“左子数组已全部合并完”，则选取右子数组元素，并且 j++
if i > left_end:
nums[k] = tmp[j]
j += 1
# 否则，若“右子数组已全部合并完”或“左子数组元素 <= 右子数组元素”，则选取左子数组元素，并且 i++
elif j > right_end or tmp[i] <= tmp[j]:
nums[k] = tmp[i]
# 左子数组区间 [left, mid], 右子数组区间 [mid+1, right]
# 创建一个临时数组 tmp ，用于存放合并后的结果
tmp = [0] * (right - left + 1)
# 初始化左子数组和右子数组的起始索引
i, j, k = left, mid + 1, 0
# 当左右子数组都还有元素时，比较并将较小的元素复制到临时数组中
while i <= mid and j <= right:
if nums[i] <= nums[j]:
tmp[k] = nums[i]
i += 1
# 否则，若“左右子数组都未全部合并完”且“左子数组元素 > 右子数组元素”，则选取右子数组元素，并且 j++
else:
nums[k] = tmp[j]
tmp[k] = nums[j]
j += 1
k += 1
# 将左子数组和右子数组的剩余元素复制到临时数组中
while i <= mid:
tmp[k] = nums[i]
i += 1
k += 1
while j <= right:
tmp[k] = nums[j]
j += 1
k += 1
# 将临时数组 tmp 中的元素复制回原数组 nums 的对应区间
for k in range(0, len(tmp)):
nums[left + k] = tmp[k]
def merge_sort(nums: list[int], left: int, right: int):