397. Integer Replacement

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?

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Example 1:

Input:
8
Output:
3

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

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Example 2:

Input:
7
Output:
4

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

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Solution:

var map = {};
map[1] = 0;
var integerReplacement = function(n) {
    if(n in map) return map[n];
    if(n % 2 === 0) map[n] = integerReplacement(n / 2) + 1;
    else map[n] = Math.min(integerReplacement(n + 1), integerReplacement(n - 1)) + 1;
    return map[n];
};