6种常见的排序算法

'''
1、冒泡排序------直接交换数值的位置
'''
def bubble_sort(alist):
    n = len(alist)
    for j in range(n-2):
         for i in range(0,n-1-j):
            if alist[i] > alist[i+1]:
              alist[i],alist[i+1] = alist[i+1],alist[i]

'''2、选择排序-----通过下标的更换实现值的交换'''
def select_sort(alist):
    n = len(alist)
    for j in range(n-1):
        min_index = j
        for i in range(j+1,n):
            if alist[min_index] > alist[i]:
                min_index = i
            alist[j],alist[min_index] = alist[min_index],alist[j]


'''3、插入算法'''
def insert_sort(alist):
    n = len(alist)
    for j in range(1,n):
        i = j
        while i > 0:
            if  alist[i] < alist[i-1]:
                alist[i],alist[i-1] = alist[i-1],alist[i]
                i -=1
            else:
                break


'''4、希尔排序------和插入排序原理相似'''
class shell_order(alist):
    n = len(alist)
    gap = n // 2
    while gap >=1:
        for j in range(gap,n):
            i = j
            while i >0:
                if alist[i] < alist[i-gap]:
                    alist[i] ,alist[i-gap] = alist[i-gap] ,alist[i]
                    i -= gap
        gap // 2

'''5、快速排序'''
class quick_sort(alist,first,last):
    if first >= last:
        return
    mid_value = alist[first]
    low = first
    high = last
    while low < high:
        while low < high and mid_value <= alist[high]:
            high -=1
        alist[low] = alist[high]
        while low < high and alist[low] < mid_value:
            low +=1
        alist[high] = alist[low]
    mid_value = alist[low]    #返回时low==high

    #对low左边的列表进行快排
    quick_sort(alist,first,low-1)
    # 对low右边的列表进行快排
    quick_sort(alist,low+1,last)

'''6、归并算法'''
class merge_sort(alist):
    n = len(alist)
    if n <= 1:
        return alist
    mid = n//2
    left_li = merge_sort(alist[:mid])
    ringht_li = merge_sort(alist[mid:])
    left_pointer,ringht_pointer = 0,0
    result = []
    while left_pointer < len(left_li) and ringht_pointer < len(ringht_li):
        if left_li[left_pointer] < ringht_li[ringht_pointer]:
            result.append(left_li[left_pointer])
            left_pointer +=1
        else:
            result.append(ringht_li[ringht_pointer])
            ringht_pointer +=1
    result += left_li[left_pointer]
    result +=ringht_li[ringht_pointer]
    return  result