Python program to Swap i’th with j’th elements in List

Last Updated : 02 May, 2023

Given a list, the task is to write a Python program to the given list of elements, toggle every i and j elements in the list.

Examples:

Input : test_list = [4, 7, 8, 0, 8, 4, 2, 9, 4, 8, 4], i, j = 4, 8
Output : [8, 7, 4, 0, 4, 8, 2, 9, 8, 4, 8]
Explanation : 4 is swapped by 8 at each occurrence.

Input : test_list = [4, 7, 8, 0, 8, 4], i, j = 4, 8
Output : [8, 7, 4, 0, 4, 8]
Explanation : 4 is swapped by 8 at each occurrence.

Method 1: Using loop + conditional statements

In this, we perform the task of toggling using conditional if-else statements, and the task of iteration is performed using a loop.

Python3

# Python3 code to demonstrate working of
# Toggle i,j elements in List
# Using loop + conditional statements
 
# initializing list
test_list = [4, 7, 8, 0, 8, 4, 2, 9, 4, 8, 4]
              
# printing original list
print("The original list is : " + str(test_list))
 
# initializing i, j 
i, j = 4, 8
 
for idx in range(len(test_list)):
     
    # perform toggling
    if int(test_list[idx]) == i:
        test_list[idx] = j
    elif int(test_list[idx]) == j:
        test_list[idx] = i
         
# printing result
print("The altered list : " + str(test_list))

Output:

The original list is : [4, 7, 8, 0, 8, 4, 2, 9, 4, 8, 4]
The altered list : [8, 7, 4, 0, 4, 8, 2, 9, 8, 4, 8]

Time Complexity: O(n)
Auxiliary Space: O(1)

Method 2: Using list comprehension + external function

In this, we perform the task of toggling using the external toggle function, and list comprehension is used to iterate through the list.

Python3

# Python3 code to demonstrate working of
# Toggle i,j elements in List
# Using list comprehension + external function
 
# external toggle 
def toggle(ele, i, j):
 
    # performing toggle
    if ele == i:
        return j
    elif ele == j:
        return i
    return ele
 
# initializing list
test_list = [4, 7, 8, 0, 8, 4, 2, 9, 4, 8, 4]
              
# printing original list
print("The original list is : " + str(test_list))
 
# initializing i, j 
i, j = 4, 8
 
# list comprehension for 1 liner
res = [toggle(ele, i, j) for ele in test_list]
         
# printing result
print("The altered list : " + str(res))

Output:

The original list is : [4, 7, 8, 0, 8, 4, 2, 9, 4, 8, 4]
The altered list : [8, 7, 4, 0, 4, 8, 2, 9, 8, 4, 8]

Time Complexity: O(n), where n is the number of elements in the list “test_list”.
Auxiliary Space: O(n), where n is the number of elements in the list “test_list”.

Method 3: Use the map() function with lambda expression.

Step-by-step approach:

Define the toggle function as a lambda expression.
Initialize the list to be modified, test_list.
Initialize the values of i and j.
Apply the map() function to the list using the lambda expression as the argument.
Convert the result of the map() function into a list.
Print the original list, the values of i and j, and the modified list

Python3

# Using map() function with lambda expression
toggle = lambda ele, i, j: j if ele == i else i if ele == j else ele
 
# initializing list
test_list = [4, 7, 8, 0, 8, 4, 2, 9, 4, 8, 4]
 
# initializing i, j 
i, j = 4, 8
 
# applying map() function to the list
res = list(map(lambda ele: toggle(ele, i, j), test_list))
 
# printing original list
print("The original list is : " + str(test_list))
 
# printing result
print("The altered list : " + str(res))

Output

The original list is : [4, 7, 8, 0, 8, 4, 2, 9, 4, 8, 4]
The altered list : [8, 7, 4, 0, 4, 8, 2, 9, 8, 4, 8]

Time complexity: O(n), where n is the length of the list, because we iterate through the entire list once.
Auxiliary space: O(n), because we create a new list to store the modified elements.