Leetcode Problem 1922. Count Good Numbers

1922. Count Good Numbers

Leetcode Solutions

Modular Exponentiation and Combinatorics

  1. Define a function modular_pow that takes a base x, an exponent y, and a modulus m and returns x^y mod m using the binary exponentiation method.
  2. Calculate the number of even indices as even_count = (n + 1) // 2.
  3. Calculate the number of odd indices as odd_count = n // 2.
  4. Compute even_result = modular_pow(5, even_count, 10^9 + 7).
  5. Compute odd_result = modular_pow(4, odd_count, 10^9 + 7).
  6. The final answer is (even_result * odd_result) mod (10^9 + 7).
  7. Return the final answer.
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Iterative Computation with Modulo

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