Leetcode 397. Integer Replacement 整数替换 解题报告

1 解题思想

这道题就是说一个数如何的以最少操作到达1，其中每个操作是：
1、若数是偶数，则可以除以2
2、如若是奇数，则现需要+1或者-1到偶数

我不知道有什么公式，直接递归搜索就可以了，注意小心边界值

2 原题

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
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.

3 AC解

public class Solution {
    /**
     * 递归搜索求解，注意他给了21474837的测试，可能会溢出，所以需要使用long)
     * */
    public int integerReplacement(int n) {
        return (int)longReplacement(n);
    }

    public long longReplacement(long n) {
        if( n < 3 ) return n - 1;
        if(n%2 ==0) return longReplacement(n/2) + 1;
        else return Math.min(longReplacement(n-1),longReplacement(n+1)) + 1;
    }
}