LeetCode 0397 - Integer Replacement

Integer Replacement

Desicription

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:

代码语言：javascript复制

Input:
8

Output:
3

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

Example 2:

代码语言：javascript复制

Input:
7

Output:
4

Explanation:
7 -> 8 -> 4 -> 2 -> 1
or
7 -> 6 -> 3 -> 2 -> 1

Solution

代码语言：javascript复制

class Solution {
private:
    std::unordered_map<long long , long long> map = std::unordered_map<long long, long long>{};
public:
    int integerReplacement(long long n) {
        if(n == 1) {
            return 0;
        }

        if(map[n] == 0) {
            if(n & 1 == 1) {
                map[n] = 2   std::min(integerReplacement((n   1) / 2), integerReplacement((n - 1) / 2));
            } else {
                map[n] = 1   integerReplacement(n / 2);
            }
        }

        return map[n];
    }
};

integer minimum replace

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