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 functiondef swapList(newList): size = len(newList) # Swapping temp = newList[0] newList[0] = newList[size - 1] newList[size - 1] = temp return newList # Driver codenewList = [12, 35, 9, 56, 24]print(swapList(newList)) |
[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 functiondef swapList(newList): newList[0], newList[-1] = newList[-1], newList[0] return newList # Driver codenewList = [12, 35, 9, 56, 24]print(swapList(newList)) |
[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 functiondef 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 codenewList = [12, 35, 9, 56, 24]print(swapList(newList)) |
[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 * operandlist = [1, 2, 3, 4]a, *b, c = listprint(a)print(b)print(c) |
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 functiondef swapList(list): start, *middle, end = list list = [end, *middle, start] return list # Driver codenewList = [12, 35, 9, 56, 24]print(swapList(newList)) |
[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 functiondef swapList(list): first = list.pop(0) last = list.pop(-1) list.insert(0, last) list.append(first) return list # Driver codenewList = [12, 35, 9, 56, 24]print(swapList(newList)) |
[24, 35, 9, 56, 12]
Approach #6: 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 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.
Python3
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 inputinp=[12, 35, 9, 56, 24]# Printing the original inputprint("The original input is:",inp)result=swap_first_last_3(inp)# Printing the resultprint("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)
