【Leetcode】397. Integer Replacement

题目链接：https://leetcode.com/contest/4/problems/integer-replacement/

题目：

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:8Output:3Explanation:8 -> 4 -> 2 -> 1

Example 2:

Input:7Output:4Explanation:7 -> 8 -> 4 -> 2 -> 1or7 -> 6 -> 3 -> 2 -> 1

UPDATE:
We have fixed the error in Integer Replacement. For input n = 3, the answer should be 2, not 3. Please try submitting again, thanks. We will rejudge your submissions after the contest finished and adjust your ranking accordingly.

思路：

easy  每遇到奇数时，分别判断n-1还是n+1的尾部零更多，越多的当然步骤越少。

特殊case：当n==Integer 最大值时，当n==3时

算法：

public int integerReplacement(int n) {if (n == Integer.MAX_VALUE)return 32;int count = 0;while (n != 1) {if ((n & 1) == 0) {n = n >> 1;count++;} else {if (n == 3)n = 2;else {if (countTrailZero(n - 1) > countTrailZero(n + 1)) {n = n - 1;} else {n = n + 1;}}count++;}}return count;}public int countTrailZero(int n) {int c = 0;while ((n & 1) == 0) {n = n >> 1;c++;}return c;}