How should I practice Largest Number Below N from Reusable Digits?

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Problem · Array

Largest Number Below N from Reusable Digits

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Problem statement

Given a positive integer n and a set of decimal digits digits, construct the largest non-negative integer that is strictly smaller than n and uses only digits from digits.

Each allowed digit may be reused any number of times. A multi-digit result cannot begin with zero, but the one-digit result 0 is valid. Return -1 when no valid result exists.

Function

largestNumberBelow(n: int, digits: int[]) → int

Examples

Example 1

n = 23415digits = [2,4,9]return = 22999

The prefix 23 cannot be continued with an allowed digit below 4, so the construction backtracks to 22 and fills the suffix with 9.

Example 2

n = 100digits = [0,1]return = 11

No valid three-digit answer is below 100, so the best two-digit construction is 11.

Constraints

1 <= n <= 10^9
1 <= digits.length <= 10
0 <= digits[i] <= 9
All values in digits are distinct.