Leetcode Problem 2376. Count Special Integers

2376. Count Special Integers

Leetcode Solutions

Digit Dynamic Programming with Bitmasking

  1. Convert the integer n to a string to process each digit individually.
  2. Initialize a DP table to memoize the results of subproblems.
  3. Define a recursive function solve that takes the current position, a tight flag, a bitmask representing used digits, and a flag for leading zeros.
  4. If the current position is at the end of the string, return 1 if the bitmask is not zero (indicating a valid special number).
  5. If the result for the current state is already computed, return it from the DP table.
  6. Iterate over possible digits for the current position, respecting the tight constraint if necessary.
  7. For each digit, calculate the new bitmask and recursively call solve for the next position.
  8. Store the result in the DP table and return the answer.
  9. Call solve for the first position with the appropriate initial conditions and subtract 1 to exclude the number n itself if it's not special.
  10. Return the final answer.
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Iterative Counting with Pruning

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