Given a positive integer n and you can do operations as follow:
If n is even, replace n with n/2.
If n is odd, you can replace n with either n + 1 or n - 1.
What is the minimum number of replacements needed for n to become 1?
Example 1:
Input:
8
Output:
3
Explanation:
8 -> 4 -> 2 -> 1
Example 2:
Input:
7
Output:
4
Explanation:
7 -> 8 -> 4 -> 2 -> 1
or
7 -> 6 -> 3 -> 2 -> 1
class Solution:
     def integerReplacement(self, n):
         """
         :type n: int
         :rtype: int
         """
         table = {}
         def helper(i):
             if i == 1:
                 return 0
             if i in table:
                 return table[i]
             if i % 2 == 0:
                 return helper(i // 2) + 1
             table[i] = min(helper(i+1), helper(i-1)) + 1
             return table[i]
         return helper(n)

class Solution:
     def integerReplacement(self, n):
         """
         :type n: int
         :rtype: int
         """
         table = {}
         def helper(i):
             if i == 1:
                 return 0
             if i in table:
                 return table[i]
             if i % 2 == 0:
                 return helper(i // 2) + 1
             table[i] = min(helper(i+1), helper(i-1)) + 1
             return table[i]
         return helper(n)
