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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0301_0400.s0397_integer_replacement;

// #Medium #Dynamic_Programming #Greedy #Bit_Manipulation #Memoization
// #2022_07_15_Time_1_ms_(66.03%)_Space_41.7_MB_(9.89%)

import java.util.HashMap;
import java.util.Map;

/**
 * 397 - Integer Replacement\.
 *
 * Medium
 *
 * Given a positive integer `n`, you can apply one of the following operations:
 *
 * 1.  If `n` is even, replace `n` with `n / 2`.
 * 2.  If `n` is odd, replace `n` with either `n + 1` or `n - 1`.
 *
 * Return _the minimum number of operations needed for `n` to become `1`_.
 *
 * **Example 1:**
 *
 * **Input:** n = 8
 *
 * **Output:** 3
 *
 * **Explanation:** 8 -> 4 -> 2 -> 1
 *
 * **Example 2:**
 *
 * **Input:** n = 7
 *
 * **Output:** 4
 *
 * **Explanation:** 7 -> 8 -> 4 -> 2 -> 1 or 7 -> 6 -> 3 -> 2 -> 1
 *
 * **Example 3:**
 *
 * **Input:** n = 4
 *
 * **Output:** 2
 *
 * **Constraints:**
 *
 * *   1 <= n <= 2³¹ - 1
**/
public class Solution {
    public int integerReplacement(int n) {
        Map dp = new HashMap<>();
        return solve(n, dp);
    }

    private int solve(int n, Map dp) {
        if (n == 1) {
            return 0;
        }
        if (dp.containsKey(n)) {
            return dp.get(n);
        }
        int ans;
        if (n % 2 == 0) {
            ans = 1 + solve(n >>> 1, dp);
        } else {
            ans = 1 + Math.min(solve(n + 1, dp), solve(n - 1, dp));
        }
        dp.put(n, ans);
        return ans;
    }
}