Given an array of integers, find the elements that appear twice. The main challenge of this problem is to solve it without using any extra space. You need to find a way to mark the elements that are already encountered. Once such way would be to make the elements negative. This post gives you 2 different solutions a video explanation.
Dynamic Programming
Problems involving dynamic programming or memoization.


Algorithmic Paradigms in short define how you can go about solving a problem. If you are starting to solve problems in computer science, this course is designed for you. However, this course is also recommended for you if you are revising all the basics and want a quick recap of some famous techniques. What are Algorithmic Paradigms? Whenever you try to build something, or develop something, an initial research and foundation is very essential. Think about it, a skyscraper will only be as stable as its base. In the world…

Dynamic programming always reminds of a favorite quotation: Of the several different ways to solve a problem, dynamic programming is a paradigm where we tend to solve the problem as we move ahead and keep on learning. This is one of the techniques which even seasoned programmers find hard to implement. In this post we will try to address some of these fears and aim to have a better understanding of this approach. If you are new to problem solving and somehow landed at this post, it is recommended to…

You are provided with an array of integers. We need to find the subarray with the maximum sum such that all the elements are contiguous. Example:Input: [2, 5, 6, 2, 3, 1, 5, 6]Output: 7Explanation: The subarray with maximum sum is [6, 2, 3, 1, 5] Problem Statement: You are provided with an array of integers. These elements could be all positive, all negative or a combination of both. A subarray is a smaller array formed using the elements of the original array. The condition for this problem is that…

Let us try to simplify the problem as much as we can. We are given with some of the terms. Weights: According to the problem each character in the English alphabet has been assigned a weight. ‘a’ has been given a weight of 1, ‘b’ has a weight of 2, and so on. The weight of ‘z’ is 26. All the letters are assumed to be lowercase for simplicity. Weight of a string: This is defined as the sum of all the characters in the string. Example if a string…

A string is said to be valid when it has only distinct characters and none of them repeat simultaneously. For example, if string ‘s two distinct characters are x and y, then valid examples could be xyxyx or yxyxy but not xxyy or xyyx.Question: Given a sample string, we need to determine what is the maximum length of valid string that can be made by deleting any of the characters.Input: beabeefeabOutput: 5 Explanation: Let us try to understand the output for the sample test case.If we delete e and f,…

Question: Given a string, find the next lexicographic permutation. Input: abcOutput: acb First of all let us try to understand what do you mean by next lexicographic string. To get a hold of the concept try to remember an English dictionary and how words are arranged in it. We start with the letter ‘a’, write all the words and then move to letter ‘b’ all the way to letter ‘z’. This is called as a lexicographic order.This is possible when we have all the letters in English alphabet available to…

Question: Given an integer N, find the prime numbers in that range from 1 to N. Input: N = 25Output: 2, 3, 5, 7, 11, 13, 17, 19, 23 We discussed the basic approaches to find the first N prime numbers in these posts Find the first N prime numbers (Method 1) Find the first N prime numbers (Method 2) It is advised that you go through the above posts to get a basic understanding of the approach that we have used to determine the prime numbers. Now lets analyze…