How to Find the Missing Number in an Array A Python Guide

Step-by-Step Guide to Finding Missing Numbers in Python

Finding the missing number in an array is a common coding interview question, especially for companies like Amazon, Adobe, Microsoft, and LinkedIn. 

Find the Missing Number in an Array A Python

This article will guide you through the process of solving this problem using Python.

Problem Statement

You are given an array containing a range of numbers from 0 to n, but with one number missing. Your task is to find the missing number in the array.

Solution Approach

To find the missing number, we can iterate over the input array and identify which number in the range is absent. Here's a step-by-step guide on how to achieve this in Python:

1. Sum Approach: Calculate the expected sum of numbers from 0 to n and subtract the sum of the given array from it.
2. XOR Approach: Use the properties of XOR to find the missing number without using extra space.
3. Set Approach: Use a set to store the numbers from 0 to n and remove the elements of the array from the set. The remaining element is the missing number.

Code :

def find_missing_number(arr):
    n = len(arr)
    total_sum = n * (n + 1) // 2  # Sum of first n natural numbers
    array_sum = sum(arr)
    missing_number = total_sum - array_sum
    return missing_number

# Example usage
array = [0, 1, 2, 4, 5]
print("The missing number is:", find_missing_number(array))

In this code :

• We calculate the expected sum of numbers from 0 to n using the formula n×(n+1)/2.
• We then calculate the sum of the given array.
• The difference between these two sums gives us the missing number.

OutPut :

The missing number is: 3

Conclusion

Finding the missing number in an array is a straightforward problem once you understand the approach. By leveraging basic arithmetic or bitwise operations, you can efficiently identify the missing element.