[LeetCode] (medium) 397. Integer Replacement

https://leetcode.com/problems/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

---

 每一步决策，注意0B11的情况（即最后要保留下那个1），最后还剩k个1时，2*(k-1)，1+k

class Solution {
public:
    int integerReplacement(int n) {
        int result = 0;
        long long num = n;
        
        while(num != 1){
            // cout << n << endl;
            ++result;
            
            if(num & 1){
                if(num & 2){
                    if(num == 3) --num;
                    else ++num;
                }
                else --num;
            }else{
                num >>= 1;
            }
        }
        
        return result;
    }
};