Statement

Given a list of integers, lst, remove all the even integers from the list.

Constraints:

$1 \leq$ lst.length $\leq 10^3$
$-10^5 \leq$ lst[i] $\leq 10^5$

Solution 1: Using list traversal

The naive approach is to traverse the list and add all the odd integers to a separate list. This results in a new list, with all the even integers removed.

Here are the steps of this solution:

Initialize a new list, odds.
Traverse through lst, and for each element in the list:
1. Append the current element to the odds list if it’s an odd integer (i.e., not divisible by 2).
Finally, return odds after all elements of lst are traversed.

Let’s look at the illustration below to better understand the solution:

Python 3.10.4

def remove_even(lst):
    odds = []
    for number in lst:  
        # Check if the item in the list is not even
        if number % 2 != 0:
            odds.append(number)  # // If it isn't even, append it to the odds list
    return odds
def main():
    inputs = [
            [3, 2, 41, 3, 34],
            [-5, -4, -3, -2, -1],
            [-1, 2, 3, -4, -10],
            [1, 2, 3, 7],
            [2, 4, 6, 8, 10],
    ]
    for i in range(len(inputs)):
        print(i + 1, ".\tInput list: ", inputs[i], sep="")
        print("\n\tFinal list: ", remove_even(inputs[i]), sep="")
        print("-" * 100)
if __name__ == "__main__":
    main()

The solution above can be made further readable using Python list comprehension.

List comprehension is a concise way to create lists in Python. It allows for the generation of new lists by applying an expression to each item in a sequence or iterable, optionally filtering items under a specified condition. The general syntax of a list comprehension is:

[new_expression for item in iterable if condition]

new_expression: This is the expression that defines how each item in the new list should be constructed from the items in the original iterable.
item: This represents the current element during each iteration through the iterable.
iterable: This is the collection of elements that the list comprehension iterates over.
condition: This is an optional part that if provided, tests each item in the iterable to decide if it should be included in the new list.

Python 3.10.4

def remove_even(lst):
    # List comprehension to iterate over list and add to a new list if not even
    return [number for number in lst if number % 2 != 0]
def main():
    inputs = [
            [3, 4, 40, 31, 32],
            [-5, -4, -6, -2, -3],
            [-1, 2, 5, -4, -10],
            [1],
            [2, 4, 6, 8, 10],
    ]
    for i in range(len(inputs)):
        print(i + 1, ".\tInput list: ", inputs[i], sep="")
        print("\n\tFinal list: ", remove_even(inputs[i]), sep="")
        print("-" * 100)
if __name__ == "__main__":
    main()

Algorithmic Paradigms

Asymptotic Analysis

Introduction to Lists

Sorting and Searching

Divide and Conquer

Conclusion

Solution: Remove Even Integers from a List

Statement

Solution 1: Using list traversal

Complexity analysis

Solution 2: Using list comprehension

Complexity analysis