DSA Problems and Solutions

1. Number of Islands problem.

Given an m x n 2D binary grid which represents a map of '1's (land) and '0's (water), return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

2. Longest Consecutive Sequence problem.

Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence. You must write an algorithm that runs in O(n) time.

3. Replicate list implementation using an array in JAVA.

3.1 TestCase

Implement a list using an array in JAVA. The list should be able to perform the following operations:

1. size.
2. isEmpty.
3. contains.
4. add.
5. remove.
6. get.
7. set.
8. clear.

4. Longest Palindromic Substring

4.1 Test Case

Given a string s, return the longest palindromic substring in s.

Input: s = "babad". Output: "bab". Note: "aba" is also a valid answer.
Input: s = "cbbd". Output: "bb".