# 歸併排序
'''歸併排序採用分而治之的原理:
1.將一個序列從中間位置分成兩個序列
2.再將兩個子序列按照第一步繼續二分下去
3.直到所有子序列的長度都爲1,也就是不可以再二分爲止,這時候再兩兩合併成一個有序序列'''
def merge(a, b):
c = []
h = j = 0
while j < len(a) and h < len(b):
if a[j] < b[h]:
c.append(a[j])
j = j + 1
else:
c.append(b[h])
h = h + 1
if j == len(a):
for i in b[h:]:
c.append(i)
else:
for i in a[j:]:
c.append(i)
return c
def merge_sort(lists):
if len(lists) <= 1:
return lists
middle = len(lists) // 2
left = merge_sort(lists[:middle])
right = merge_sort(lists[middle:])
return merge(left, right)
if __name__ == '__main__':
a = [12, 3, 89, 6, 54, 54, 87]
print(merge_sort(a))