397. Integer Replacement

Problem:

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：

Solution (C++):

unordered_map<int, int> visited;
int integerReplacement(int n) {
    if (n == 1)  return 0;
    if (visited.count(n) == 0) {
        if (n & 1 == 1)
            visited[n] =  2 + min(integerReplacement(n/2), integerReplacement(n/2+1));               
        else 
            visited[n] = 1 + integerReplacement(n/2);
    }
    return visited[n];
}

性能：

Runtime: 0 ms  Memory Usage: 9.7 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB