Katkat
Back

Count Three-Digit Numbers With All-Distinct Digits in a Range

Capital OneSoftware Engineer · Online Assessment
MediumSoftware EngineerOnline AssessmentCoding & Algorithms

Last updated

A coding question that asks you to count the three-digit integers in an inclusive range whose hundreds, tens and units digits are all different from one another. It tests digit extraction, inclusive range boundaries and treating zero digits like any other digit.

Given two three-digit integers left and right, count how many integers in the inclusive range from left to right have three pairwise different digits, that is, no digit appears more than once in the number.

Function Signature

def count_distinct_digit_numbers(left: int, right: int) -> int:

Rules

  • Both left and right belong to the range.
  • A number qualifies only when its hundreds, tens and units digits are three different digits. A zero digit is treated like any other digit: 890 qualifies, while 900 and 808 do not.
  • Return the count as a single integer, or 0 when no number in the range qualifies.

Constraints

  • 100 <= left <= right <= 999

Examples

Example 1

Input: left = 876, right = 890
Output: 3

Only 876, 879 and 890 qualify. 877 and 878 repeat a digit, and every number from 880 to 889 repeats the digit 8.

Example 2

Input: left = 100, right = 110
Output: 8

102 through 109 qualify; 100, 101 and 110 each repeat a digit.

Example 3

Input: left = 987, right = 999
Output: 1

Only 987 qualifies.