leetcode397.Integer Replacement

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题目要求

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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

思路和代码

可以发现除二后所得到的结果一定优于加减1。因此，如果当前奇数除二为偶数，则直接做除法，否则将当前奇数加一再除以二，得到偶数的结果。

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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;
}