Python program to interchange first and last elements in a list

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

Examples:

Input : [12, 35, 9, 56, 24]
Output : [24, 35, 9, 56, 12]

Input : [1, 2, 3]
Output : [3, 2, 1]

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

Python3

# Python3 program to swap first
# and last element of a list

# 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))

Output:

[24, 35, 9, 56, 12]

Approach #2: The last element of the list can be referred as list[-1]. Therefore, we can simply swap list[0] with list[-1].

Python3

# Python3 program to swap first
# and last element of a list

# Swap function
def swapList(newList):

    newList[0], newList[-1] = newList[-1], newList[0]

    return newList

# Driver code
newList = [12, 35, 9, 56, 24]
print(swapList(newList))

Output:

[24, 35, 9, 56, 12]

Time Complexity: O(1)
Auxiliary Space: O(n), where n is length of list

Approach #3: 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. 

Python3

# Python3 program to swap first
# and last element of a list

# 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))

Output:

[24, 35, 9, 56, 12]

Approach #4: 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. 

Python3

# Python3 program to illustrate
# the usage of * operand
list = [1, 2, 3, 4]

a, *b, c = list

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

Output:

1
[2, 3]
4

Now let’s see the implementation of above approach: 

Python3

# Python3 program to swap first
# and last element of a list

# 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))

Output:

[24, 35, 9, 56, 12]

Approach #5: Swap the first and last elements is to use the inbuilt function list.pop(). Pop the first element and store it in a variable. Similarly, pop the last element and store it in another variable. Now insert the two popped element at each other’s original position. 

Python3

# Python3 program to swap first
# and last element of a list

# Swap function
def swapList(list):

    first = list.pop(0)
    last = list.pop(-1)

    list.insert(0, last)
    list.append(first)

    return list

# Driver code
newList = [12, 35, 9, 56, 24]

print(swapList(newList))

Output:

[24, 35, 9, 56, 12]