Python - 冒泡排序

Question

Hi I reviewed other posts with bubble sort, but solution didn't work in my case: So algorithm works until I repeat few times while loop. But how can I do this without using input? Here is my code so you know what I mean:

x = [0, 0, 1, 3, 3, 2, 2, 1, 0, 4, 5]

h = None
flag = True

while flag == True:
    #flag = True
    for i in range(len(x) - 1):
        if x[i] > x[i + 1]:
    #       flag = False
            h = x[i]
            x[i] = x[i + 1] 
            x[i + 1] = h
    print(x)        

    #input = raw_input('Satisfied? ')
    #if input == 'q':
    #   break

print(x)
'''
we can replace variable h, with:
x[i] , x[i+1] = x[i+1], x[i]
'''

Answer 1

You can make use of the sorted function in python, and change your code to be:

while flag == True:
    for i in range(len(x) - 1):
        if x[i] > x[i + 1]:
            h = x[i]
            x[i] = x[i + 1] 
            x[i + 1] = h

    if sorted(x) == x: #x is already sorted
        flag = False

Edit: Alternate solution which doesn't use python's built in sort function:

while flag == True:
    flag = False
    for i in range(len(x) - 1):
        if x[i] > x[i + 1]:
            flag = True
            h = x[i]
            x[i] = x[i + 1] 
            x[i + 1] = h

Hope I helped!

Answer 2

With this algorithm, you can previously know how many steps (max) are needed to sort the whole array, because the algorithm is convergent and bounded. In each pass, the highest no-placed value is placed correctly, so you will need n-1 passes to complete the sorting.

Here an example:

mylist = [54,26,93,17,77,31,44,55,20]

for num in range(len(mylist)-1, 0, -1):
    for i in range(num):
        if mylist[i] > mylist[i+1]:
            aux = mylist[i]
            mylist[i] = mylist[i+1]
            mylist[i+1] = aux


print(mylist)

Hope it helps

PS: What you intended to do, stopping when the list is sorted before the n-1 pass, is better done with the "insertion algorithm". Here there is an interesting comparision between insertion and bubble sorting: Insertion sort vs Bubble Sort Algorithms

Answer 3

I little refactor for your code:

for num in range(len(mylist)-1, 0, -1):
    for i in range(num):
        if mylist[i] > mylist[i+1]:
            mylist[i], mylist[i+1] = mylist[i+1], mylist[i]

Answer 4

Python recursive bubble sort

def bubble_f(lst):
    if len(lst) < 2:
        return lst

    if lst[0] > lst[1]:
        return [lst[1]] + bubble_f([lst[0]] + lst[2:])

    return [lst[0]] + bubble_f([lst[1]] + lst[2:])

def bubble_sort(lst):
    if len(lst) < 2:
        return lst

    sorted = bubble_f(lst)

    return bubble_sort(sorted[:-1]) + [sorted[-1]]

list1 = [5, 9, 23, 4, 3, 8, 1, 12, 2, 9, 15, 19, 11, 27, 0]
print(bubble_sort(list1))