LeetCode 268 Missing Number in Python | Easy Coding Tutorial for Beginners
Solve LeetCode 268 "Missing Number" in Python with this beginner-friendly coding tutorial! This problem asks you to find the missing number in an array of distinct integers from 0 to `n`, where `n` is the length of the array (e.g., nums = [3,0,1], return 2). We’ll use the mathematical formula for the sum of the first `n` natural numbers and subtract the sum of the array to find the missing number in one line. Perfect for Python learners, coding beginners, or anyone prepping for coding interviews!
🔍 *What You'll Learn:*
Understanding LeetCode 268’s requirements
Using the sum of an arithmetic sequence to find the expected sum
Subtracting the array sum to identify the missing number
Testing with example cases
💻 *Code Used in This Video:*
class Solution(object):
def missingNumber(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
n = len(nums)
return n * (n+1) // 2 - sum(nums)
Test cases
solution = Solution()
Test case 1: Missing number in the middle
print(solution.missingNumber([3, 0, 1])) # Output: 2
n = 3, expected sum = 0+1+2+3 = 6, actual sum = 3+0+1 = 4, missing = 6-4 = 2
Test case 2: Missing number at the end
print(solution.missingNumber([0, 1, 2, 3])) # Output: 4
n = 4, expected sum = 0+1+2+3+4 = 10, actual sum = 0+1+2+3 = 6, missing = 10-6 = 4
Test case 3: Missing number at the beginning
print(solution.missingNumber([1, 2, 3, 4])) # Output: 0
n = 4, expected sum = 0+1+2+3+4 = 10, actual sum = 1+2+3+4 = 10, missing = 10-10 = 0
Test case 4: Single element
print(solution.missingNumber([0])) # Output: 1
n = 1, expected sum = 0+1 = 1, actual sum = 0, missing = 1-0 = 1
🌟 *Why Solve LeetCode 268?*
This problem is a great introduction to mathematical techniques in coding, a common topic in coding interviews! We’ll show how `n * (n+1) // 2 - sum(nums)` uses the formula for the sum of the first `n` natural numbers to find the missing number efficiently. The time complexity is O(n) due to the sum operation, and the space complexity is O(1). Master this, and you’ll be ready for more advanced LeetCode challenges!
📚 *Who’s This For?*
Python beginners learning coding
Coding enthusiasts tackling LeetCode problems
Developers prepping for technical interviews
👍 Like, subscribe, and comment: What LeetCode problem should we solve next? Next up: More LeetCode array problems—stay tuned!
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