Logic Building
# Take array
n = int(input("Enter n (expected range 1 to n): "))
arr = []
for i in range(n - 1):
arr.append(int(input(f"Element {i+1}: ")))
# Calculate expected sum
expected_sum = n * (n + 1) // 2
actual_sum = sum(arr)
missing = expected_sum - actual_sum
print(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
Use sum formula to find missing number.
Key Concepts:
- Expected sum = n*(n+1)/2
- Actual sum from array
- Missing = expected - actual