Integer replacement

We will follow the problem statement, and solve it recursively. Then we will memoize the result to avoid repeated computations.

class Solution:
    def integerReplacement(self, n: int) -> int:
        def _calculate(n, memo):
            if n in memo:
                return memo[n]

            if n == 1:
                return 0

            if n%2 == 0:
                memo[n] = 1 + _calculate(n/2, memo)
            else:
                memo[n] = 1 + min(_calculate(n+1, memo), _calculate(n-1, memo))

            return memo[n]

        return _calculate(n, {})

Time complexity: O(n)
Space complexity: O(n)