Python program to interchange first and last elements in a list

Given a list, write a Python program to swap the first and last element of the list using Python.

Examples: The last element of the list can be referred to as a list[-1]. Therefore, we can simply swap list[0] with list[-1].

# Initialize a list
my_list = [1, 2, 3, 4, 5]

# Interchange first and last elements
my_list[0], my_list[-1] = my_list[-1], my_list[0]

# Print the modified list
print("List after swapping first and last elements:", my_list)

Output

List after swapping first and last elements: [5, 2, 3, 4, 1]

Interchange first and last elements using Temporary Value

Find the length of the list and simply swap the first element with (n-1)^th element.

# Swap function
def swapList(newList):
    size = len(newList)
    
    # Swapping 
    temp = newList[0]
    newList[0] = newList[size - 1]
    newList[size - 1] = temp
    
    return newList
    
# Driver code
newList = [12, 35, 9, 56, 24]

print(swapList(newList))

[24, 35, 9, 56, 12]

Swapping first and last items in a list using tuple variable

Swap the first and last element is using tuple variable. Store the first and last element as a pair in a tuple variable, say get, and unpack those elements with first and last element in that list. Now, the First and last values in that list are swapped. 

# Swap function
def swapList(list):
    
    # Storing the first and last element 
    # as a pair in a tuple variable get
    get = list[-1], list[0]
    
    # unpacking those elements
    list[0], list[-1] = get
    
    return list
    
# Driver code
newList = [12, 35, 9, 56, 24]
print(swapList(newList))

[24, 35, 9, 56, 12]

Swap first and last values in a list in Python using * operand

This operand proposes a change to iterable unpacking syntax, allowing to specify a “catch-all” name which will be assigned a list of all items not assigned to a “regular” name. 

list = [1, 2, 3, 4]

a, *b, c = list

print(a)
print(b)
print(c)

1
[2, 3]
4

Now let’s see the implementation of above approach: 

# Swap function
def swapList(list):
    
    start, *middle, end = list
    list = [end, *middle, start]
    
    return list
    
# Driver code
newList = [12, 35, 9, 56, 24]

print(swapList(newList))

[24, 35, 9, 56, 12]

Swap first and last values in a list in Python using Slicing

In this approach, we first check if the list has at least 2 elements. If the list has at least 2 elements, we swap the first and last elements using Python slicing by assigning the value of the last element to the first element and the value of the first element to the last element. We then slice the list from the second element to the second-to-last element and concatenate it with a list containing the first element and the last element in their new positions.

def swap_first_last_3(lst):
    # Check if list has at least 2 elements
    if len(lst) >= 2:
        # Swap the first and last elements using slicing
        lst = lst[-1:] + lst[1:-1] + lst[:1]
    return lst

# Initializing the input
inp=[12, 35, 9, 56, 24]

# Printing the original input
print("The original input is:",inp)

result=swap_first_last_3(inp)

# Printing the result
print("The output after swap first and last is:",result)

The original input is: [12, 35, 9, 56, 24]
The output after swap first and last is: [24, 35, 9, 56, 12]

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