Python Coding challenge - Day 540| What is the output of the following Python Code?

 

Code Explanation:

Function Definition

def two_sum(nums, target):

Purpose: This defines a function named two_sum that takes two parameters:

nums: a list of integers

target: the target sum we want to find from the sum of two elements in nums.

Initialize Lookup Dictionary

    lookup = {}

Purpose: This creates an empty dictionary called lookup.

Use: It will store numbers as keys and their indices as values.

Goal: Quickly check if the complement (i.e., target - num) of the current number has already been seen.

Loop Through the List

    for i, num in enumerate(nums):

Purpose: Iterates over the list nums using enumerate, which provides:

i: the index of the current element

num: the value of the current element

Check for Complement in Lookup

        if target - num in lookup:

Purpose: Checks whether the difference between the target and the current number (target - num) exists in the lookup dictionary.

Why: If this complement exists, it means the current number and the complement add up to the target.

Return the Indices of the Two Numbers

            return [lookup[target - num], i]

Purpose: If the complement is found, return the index of the complement (from the dictionary) and the current index i as a list.

Result: This list represents the indices of the two numbers that add up to the target.

Store Current Number in Lookup

        lookup[num] = i

Purpose: Adds the current number as a key to the lookup dictionary, with its index as the value.

Why: So it can be used later if its complement appears in the future iterations.

Function Call and Output

print(two_sum([2, 7, 11, 15], 9))

Purpose: Calls the function with the list [2, 7, 11, 15] and target = 9.

Expected Output: [0, 1] because nums[0] + nums[1] = 2 + 7 = 9.

Final Output:

[0, 1]

Download Book-500 Days Python Coding Challenges with Explanation