life is too short for a diary

Given a string s and an array of strings words, return the number of words[i] that is a subsequence of s. A subsequence of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters...

Continue reading → leetcode java

Design a time-based key-value data structure that can store multiple values for the same key at different time stamps and retrieve the key's value at a certain timestamp...

Continue reading → java leetcode

Continue reading → leetcode java

Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure...

Continue reading → leetcode java python design

A sentence is a string of single-space separated words where each word can contain digits, lowercase letters, and the dollar sign '$'. A word represents a price if it is a sequence of digits preceded by a dollar sign...

Continue reading → leetcode java python string

Given a string s, sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string...

Continue reading → leetcode java python heap

An interesting problem on leetcode to find minimum number of ways to pick up consecutive cards. We will start with a brute force algorithm that would exceed in time limit. Later we will improve upon this algorithm using hashmap...

Continue reading → leetcode java python hashmap

You are given a **0-indexed** binary array `nums` of length `n`. `nums` can be divided at index `i` (where `0 <= i <= n`) into two arrays (possibly empty) nums_{left} and nums_{right}..

Continue reading → leetcode hashmap array java python

In this [leetcode](https://leetcode.com/problems/longest-substring-without-repeating-characters/) problem, we are asked to find the length of the longest string of characters in a provided string that does not contain repeating characters. In other words, in the string `abcabcbb` the longest substring without repeating characters is `abc` (with a length of 3)...

Continue reading → leetcode two pointers set string

There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [a_{i}, b_{i}] indicates that you must take course b_{i} first if you want to take course a_{i}...

Continue reading → leetcode graph bfs java python

You are given a string s and an integer k, a k duplicate removal consists of choosing k adjacent and equal letters from s and removing them, causing the left and the right side of the deleted substring to concatenate together...

Continue reading → leetcode stack python java scala javascript

Questions involving the binary tree data structure are very popular in tech interviews, and can be challenging and varied! A binary tree is a data structure consisting of a collection of nodes (starting at a root node), where each node consists of a value (data), together with a directed edges to at most two nodes (the "left child" and "right child"), with the additional conditions that no two edges point to the same node and no edge points to the root. I recently solved an interesting problem on binary tree...

Continue reading → leetcode java python javascript scala

It's one of the most popular questions on leetcode that seems very easy at first. Coin change is a classic dynamic programming problem. I will proceed with an obvious (albeit wrong) solution and subsequently proceed to an efficient correct solution...

Continue reading → leetcode dp java python

There's an interesting problem I recently solved on leetcode based on dynamic programming. My Github repository contains list of all problems that I have solved. I often start with a brute force approach without fretting about time complexity. Later I try to improve my algorithm for a better efficient solution...

Continue reading → leetcode dp java python

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists...

Continue reading → programming leetcode code

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero...

Continue reading → leetcode two pointers java