[LeetCode] Integer Replacement

Problem

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

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

Note

记一种简单的iteration的做法：
先讨论边界case，若n为Integer最大值，返回32.
然后对整数n分奇偶两种情况讨论，偶数除以2，奇数判断是否+1后能被4整除且n不等于3，若如此则+1，否则-1. 每次操作后计数器+1，循环结束后返回计数器值。

Solution

public class Solution {
    public int integerReplacement(int n) {
        if (n == Integer.MAX_VALUE) return 32;
        int count = 0;
        while (n != 1) {
            if (n%2 == 0) n/=2;
            else {
                if ((n+1)%4==0 && n!=3) n+=1;
                else n-=1;
            }
            count++;
        }
        return count;
    }
}