Given a list in Python and provided the positions of the elements, write a program to swap the two elements in the list.
Examples:
Input : List = [23, 65, 19, 90], pos1 = 1, pos2 = 3
Output : [19, 65, 23, 90]Input : List = [1, 2, 3, 4, 5], pos1 = 2, pos2 = 5
Output : [1, 5, 3, 4, 2]
Swap Two Elements in a List using comma assignment
Since the positions of the elements are known, we can simply swap the positions of the elements.
Python3
# Python3 program to swap elements# at given positions# Swap functiondef swapPositions(list, pos1, pos2): list[pos1], list[pos2] = list[pos2], list[pos1] return list# Driver functionList = [23, 65, 19, 90]pos1, pos2 = 1, 3print(swapPositions(List, pos1-1, pos2-1)) |
Output:
[19, 65, 23, 90]
Time Complexity: O(1), for using constant operations.
Auxiliary Space: O(1), for using constant extra space.
Using Inbuilt list.pop() function to Swap Two Elements in a List
Pop the element at pos1 and store it in a variable. Similarly, pop the element at pos2 and store it in another variable. Now insert the two popped element at each other’s original position.
Python3
# Python3 program to swap elements# at given positions# Swap functiondef swapPositions(list, pos1, pos2): # popping both the elements from list first_ele = list.pop(pos1) second_ele = list.pop(pos2-1) # inserting in each others positions list.insert(pos1, second_ele) list.insert(pos2, first_ele) return list# Driver functionList = [23, 65, 19, 90]pos1, pos2 = 1, 3print(swapPositions(List, pos1-1, pos2-1)) |
Output:
[19, 65, 23, 90]
Time Complexity: O(1), for using constant operations.
Auxiliary Space: O(1), for using constant extra space.
Swap Two Elements in a List Using tuple variable
Store the element at pos1 and pos2 as a pair in a tuple variable, say get. Unpack those elements with pos2 and pos1 positions in that list. Now, both the positions in that list are swapped.
Python3
# Python3 program to swap elements at# given positions# Swap functiondef swapPositions(list, pos1, pos2): # Storing the two elements # as a pair in a tuple variable get get = list[pos1], list[pos2] # unpacking those elements list[pos2], list[pos1] = get return list# Driver CodeList = [23, 65, 19, 90]pos1, pos2 = 1, 3print(swapPositions(List, pos1-1, pos2-1)) |
Output:
[19, 65, 23, 90]
Time Complexity: O(1), for using constant operations.
Auxiliary Space: O(1), for using constant extra space.
Swap Two Elements in a List Using temp variable
Python3
# Python3 program to swap elements# at given positions# Swap functiondef swapPositions(lis, pos1, pos2): temp=lis[pos1] lis[pos1]=lis[pos2] lis[pos2]=temp return lis# Driver functionList = [23, 65, 19, 90]pos1, pos2 = 1, 3print(swapPositions(List, pos1-1, pos2-1)) |
[19, 65, 23, 90]
Time Complexity: O(1), for using constant operations.
Auxiliary Space: O(1), for using constant extra space.
Swap Two Elements in a List Using enumerate
Another approach to swapping elements in a list is to use the enumerate function to get the index and value of each element in the list, and then use a loop to find the elements that need to be swapped and swap them.
Python3
def swapPositions(lis, pos1, pos2): for i, x in enumerate(lis): if i == pos1: elem1 = x if i == pos2: elem2 = x lis[pos1] = elem2 lis[pos2] = elem1 return lisList = [23, 65, 19, 90]pos1, pos2 = 1, 3print(swapPositions(List, pos1-1, pos2-1))#This code is contributed by Edula Vinay Kumar Reddy |
[19, 65, 23, 90]
This approach has a time complexity of O(n), since it involves looping through the entire list to find the elements to be swapped. The space complexity is O(1), since it only uses a constant amount of additional space to store the elements to be swapped.
Note that this approach can be made more efficient by using a single loop and breaking out of the loop once the elements have been found and swapped.
