leetcode397. Integer Replacement

題目要求

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 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

思路和代碼

能夠發現除二後所獲得的結果必定優於加減1。所以，若是當前奇數除二爲偶數，則直接作除法，不然將當前奇數加一再除以二，獲得偶數的結果。

public int integerReplacement(int n) {
        int count = 0;
        while(n != 1){
            if((n & 1) == 0){
                n >>>= 1;
            }
            else if(n == 3 || ((n>>>1) & 1) == 0){
                n--;
            }
            else{
                n++;
            }
            count++;
        }
        return count;
    }

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