Program to swap positions of items in list not working with all test cases-CodePudding

I'm writing a simple Python program that swaps the positions of the smallest and largest values in a user-inputted list. The code is as follows:

def swap_min_max(a_list): # a_list here is called formal parameter     
    min = 1
    max = 0
   
    for i in a_list:
        if i > max:
            max = i
        elif i < min:
            min = i
    
    for i in range(len(a_list)):
        if a_list[i] == max:
            a_list[i] = min

        elif a_list[i] == min:
            a_list[i] = max

a_list = [int(str_numbers) for str_numbers in input().split() ] # Input list creation via list comprehension
swap_min_max(a_list)
print(*a_list)

The code has no issues that I can identify, but it does not work with all test cases - for example, inputting 3 4 5 2 1 yields the desired output of 3 4 1 2 5, but inputting 20 50 10 30 70 40 yields 20 50 10 30 1 40 rather than the expected output of 20 50 70 30 10 40. Although I can see that this is related to my min and max variables at the beginning of the function definition, I'm unsure why this issue only arises in some cases.

CodePudding user response：

min and max are built-in python functions. You can use these functions to find the minimum/maximum of a list, then get the index of the elements, and swap them.

def swap_min_max(a_list): # a_list here is called formal parameter     
    minVal = min(a_list)
    maxVal = max(a_list)
    
    minIndex = a_list.index(minVal)
    maxIndex = a_list.index(maxVal)
    
    a_list[minIndex], a_list[maxIndex] = a_list[maxIndex], a_list[minIndex]

   

a_list = [int(str_numbers) for str_numbers in input().split() ] # Input list creation via list comprehension

swap_min_max(a_list)
print(*a_list)

You can turn this into a messy one-liner with:

a_list[a_list.index(min(a_list))], a_list[a_list.index(max(a_list))] = a_list[a_list.index(max(a_list))], a_list[a_list.index(min(a_list))]

Input of 20 50 10 30 70 40

Returns 20 50 70 30 10 40

CodePudding user response：

def swap(alist):
    mx, max_idx = max(alist), alist.index(max(alist))
    mn, min_idx = min(alist), alist.index(min(alist))

    alist[min_idx] = mx
    alist[max_idx] = mn

    return alist
swap(a_list)

returns [20, 50, 70, 30, 10, 40]