Leetcode Problem 2801. Count Stepping Numbers in Range

2801. Count Stepping Numbers in Range

Leetcode Solutions

Digit Dynamic Programming (DP) Approach

  1. Define a recursive function countStepNums with parameters: current index, tightness, leading zeros, previous digit, and the DP table.
  2. If the current index equals the length of the string, return 1 if it's a valid stepping number, else return 0.
  3. If the DP table entry for the current state is not -1, return the stored value.
  4. Calculate the upper bound for the current digit based on tightness.
  5. Iterate over all possible digits for the current index, and for each: a. If the previous digit is not -1 and there are no leading zeros, ensure the current digit differs from the previous by 1. b. Recursively call countStepNums for the next index with updated parameters. c. Sum the results of the recursive calls.
  6. Store the result in the DP table and return it.
  7. Call countStepNums for the range from 0 to low and from 0 to high.
  8. Subtract the result for low from the result for high and adjust for inclusivity of low if it's a stepping number.
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Breadth-First Search (BFS) Approach

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