LeetCode 397. Integer Replacement

Posted 2020-08-12

397. Integer Replacement

 

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• Total Accepted: 5878
• Total Submissions: 21519
• Difficulty: Easy

 

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

 

 

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这个题目没思路，参考了别人的想法  网址：https://discuss.leetcode.com/topic/58334/a-couple-of-java-solutions-with-explanations

class Solution {
public:
    int integerReplacement(int n) {
        if(INT_MAX==n)return 32;   //INT_MAX是个特殊值，如果加1就越界了
        //我们也可以用long long 类型的数令它等于n，如 long long N=n;然后把下面的n替换成N即可

        int c = 0;
        while (n != 1) {
            if ((n & 1) == 0) {
                n /= 2;
            }
            else if (n == 3 || ((n) & (1<<1)) == 0) {     //留意后两位 奇数是最后一位是1 如果倒数第二位是0那么减1 使得1的位数更少
                --n;
            }
            else {
                ++n;
            }
            ++c;
        }
        return c;
    }
};