[LintCode/LeetCode] Integer Replacement

Problem

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

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

Solution

public class Solution {
    /**
     * @param n: a positive integer 
     * @return: the minimum number of replacements
     */
    public int integerReplacement(int n) {
        // Write your code here
        if (n == 1) return 0;
        if (n == Integer.MAX_VALUE) return 32;
        int count = 0;
        while (n > 1) {
            if (n % 2 == 0) {
                n /= 2;
                count++;
            } else {
                if ((n+1) % 4 == 0 && n != 3) {
                    n++;
                    count++;
                } else {
                    n--;
                    count++;
                }
            }
        }
        return count;
    }
}
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