leetcode 397. Integer Replacement

发表于 | 分类于

Given a positive integer n and you can do operations as follow:

  1. If n is even, replace n with n/2.
  2. If n is odd, you can replace n with eithern + 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

  • clear solution:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
class Solution(object):
    def integerReplacement(self, n):
        """
        :type n: int
        :rtype: int
        """
        d = {}
        def helper(n):
            if n == 1:
                return 0
            if n in d:
                return d[n]
            val = 0
            if n%2 == 0:
                val = 1 + helper(n/2)
            else:
                val = min(1+helper(n-1),1+helper(n+1))
            d[n] = val
            return val
        return helper(n)
  • my solution:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
class Solution(object):
    def integerReplacement(self, n):
        """
        :type n: int
        :rtype: int
        """
        def helper(n):
            if n == 1:
                return 0
            if n == 3:
                return 2
            val = 0
            if n%2 == 0:
                val = 1 + helper(n/2)
            else:
                val = min(1+helper(n-1),1+helper(n+1))
           
            return val
        return helper(n)

my solution recursion do not store ,slower than clear solution