Next
1. Check if Array is Sorted (Ascending)2. Check if Array is Sorted (Descending)3. Find Second Largest4. Find Second Smallest5. Range (Max - Min)6. Sum Except Max & Min7. Count Pairs with Sum K8. Count Elements Greater Than Average9. Frequency of Distinct Elements10. Unique Elements Only11. Find Kth Largest Element12. Rotate Array by K Positions13. Find Missing Number in Sequence14. Find Duplicate Element

Find Missing Number in Sequence

Find missing number in array containing 1 to n with one missing.

AdvancedPhase 4 - Level 5: Logical & AppliedExample 13 of 14
find-missing-number-in-sequence.py
1# Take array
2n = int(input("Enter n (expected range 1 to n): "))
3arr = []
4for i in range(n - 1):
5    arr.append(int(input(f"Element {i+1}: ")))
6

7# Calculate expected sum
8expected_sum = n * (n + 1) // 2
9actual_sum = sum(arr)
10missing = expected_sum - actual_sum
11

12print(f"Missing number: {missing}")

Output

Enter n (expected range 1 to n): 5
Element 1: 1
Element 2: 2
Element 3: 4
Element 4: 5
Missing number: 3

What's going on

Use sum formula to find missing number.

Key Concepts:

Expected sum = n*(n+1)/2
Actual sum from array
Missing = expected - actual

🔗Related Content

PreviousRotate Array by K PositionsNextFind Duplicate Element