## Solved! Leetcode 2405. Optimal Partition of String

source: https://leetcode.com/problems/optimal-partition-of-string/description/ Optimal Partition of String Given a string s, partition the string into one or more substrings such that the characters in each substring are unique. That is, no letter appears in a single substring more than once. Return the minimum number of substrings in such a partition. Note that each character should belong ...

## Solved! Leetcode 1345. Jump Game IV

source: https://leetcode.com/problems/jump-game-iv/description/ Jump Game IV Given an array of integers arr, you are initially positioned at the first index of the array. In one step you can jump from index i to index: i + 1 where: i + 1 < arr.length. i – 1 where: i – 1 >= 0. j where: arr[i] == ...

## Solved! Leetcode 491: Non-decreasing Subsequences

https://leetcode.com/problems/non-decreasing-subsequences/description/ Given an integer array nums, return all the different possible non-decreasing subsequences of the given array with at least two elements. You may return the answer in any order. Example 1: Input: nums = [4,6,7,7] Output: [[4,6],[4,6,7],[4,6,7,7],[4,7],[4,7,7],[6,7],[6,7,7],[7,7]] class Solution { public List<List<Integer>> findSubsequences(int[] nums) { Set<List<Integer>> res = new HashSet<>(); helper(nums, 0, new ArrayList<>(), res); return new ...

## Null Keys or values in HashMap/Hashtable4

Can java.util.HashMap store null key/value pair? Yes it can, However only one null key is allowed, but can store many null values against non-null keys   Example public class HashMapTest { public static void main(String args[]) { HashMap h = new HashMap(); h.put(null,null); h.put(null, "1"); h.put("1", null); h.put("1", "1"); h.put("2", null); System.out.println(h.get(null).toString()); System.out.println(h.get("1")); System.out.println(h.get("2")); } ...

## Hashmap and Hashtable

The HashMap class is roughly equivalent to Hashtable, except that it is non synchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesn’t allow nulls). However, HashMap can be synchronized using Map m = Collections.synchronizeMap(hashMap); Hashtable and HashMap are member of the Java Collections Framework (since Java 2 platform v1.2, ...