Sunday, October 30, 2016

Integer Replacement

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 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

The most straightforward way is to use recursion. Recursively calculate number of replacement needed until integer reaches 1.  

public int integerReplacement(int n) {
        return getCount(n, 0);
    }
    
    private int getCount(long n, int count) {
        if (n == 1) {
            return count;
        }
        
        count++;
        if (n % 2 == 0) {
            return getCount(n / 2, count);
        } else {
            return Math.min(getCount(n - 1, count), getCount(n + 1, count));
        }
    }


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