冒泡排序及其优化

题目

代码

原始排序

def bubbleSort(alist):
    for i in range(len(alist)):
        for j in range(len(alist) - i -1):
            if alist[j] > alist[j+1]:
                alist[j], alist[j+1] = alist[j+1] , alist[j]
    return alist

第一次改进

def bubbleSort2(alist):
    flag = False  # 设置标记
    for i in range(len(alist)):
        for j in range(len(alist) - i -1):
            if alist[j] > alist[j+1]:
                alist[j], alist[j+1] = alist[j+1] , alist[j]
                flag = True  # 只要还能排序就置True
        if  not flag:   # 排序好后就停止
            return alist
    return alist

第二次改进

def bubbleSort3(alist):   
    count = len(alist)
    for i in range(count):
        for j in range(i+1, count):  # 每次循环只从未排序的序列中取出第一个数
            if alist[i] > alist[j]:
                alist[i], alist[j] = alist[j], alist[i]
    return alist

调用

alist = list(map(int,input("Enter a list:").split( )))

after_sort_list = bubbleSort(alist)
after_sort_list2 = bubbleSort2(alist)
after_sort_list3 = bubbleSort3(alist)

print(after_sort_list)
print(after_sort_list2)
print(after_sort_list3)

输入

Enter a list:1 4  2  3

输出

[1, 2, 3, 4]
[1, 2, 3, 4]
[1, 2, 3, 4]