Hiring process8 levels
  1. 1 IQ Test
  2. 2 Additional Online Test (If Required)
  3. 3 Office Interview with Hiring Manager
  4. 4 Unpaid Test Task (Motivation Check)
  5. 5 Paid Test Task and Follow-Up Interview
  6. 6 Iterative Paid Test Tasks
  7. 7 Office Verification
  8. 8 Final Interview with the Founder

Problems > Counting a Digit > Editorial

Counting a Digit — Solution & Editorial

Back to the Problem

Position-by-position counting: split N around each digit position into (high, current, low) and count how often D occupies that position; D = 0 needs the leading-zero adjustment.

Complexity: O(log N)

Watch out: Zero never appears as a leading digit — its count needs the high > 0 correction.