Permutation – position (order) matters. = N! / (N – r)!. Building words with {a,b,c} are also permutation problem with r = {1,2,3..N} Combination – position (order) doesn’t matter = N! / (N – r)! * r! . Combination is a part of Permutation set. All possible combination means, generating combination for r = {0,1.. […]

## System Design links

https://github.com/donnemartin/system-design-primer

## Important and Useful links from all over the Leetcode

List of all good posts on Leetcode. Comment down whichever I am missing and I will add all of them here – DP for beginners by @wh0ami – https://leetcode.com/discuss/general-discussion/662866/dp-for-beginners-problems-patterns-sample-solutions[LIST – https://leetcode.com/list/x1k8lxi5] Graph for beginners by @wh0ami – https://leetcode.com/discuss/general-discussion/655708/graph-for-beginners-problems-pattern-sample-solutions/562734[LIST – https://leetcode.com/list/x1wy4de7] Sliding window for beginners by @wh0ami – https://leetcode.com/discuss/general-discussion/657507/sliding-window-for-beginners-problems-template-sample-solutions/562721[LIST – https://leetcode.com/list/x1lbzfk3] DP Patterns by @aatalyk – https://leetcode.com/discuss/general-discussion/458695/dynamic-programming-patterns Leetcode patterns from edu_cative_dot_io by @late_riser […]

## Leetcode – 78. Subsets

Given a set of distinct integers, nums, return all possible subsets (the power set). Note: The solution set must not contain duplicate subsets. Solution:

## .NET Big O Algorithm Complexity Cheat-Sheet

## Leetcode 99 – Recover Binary Search Tree – Constant space

Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure with constant space. Example 1: Input: [1,3,null,null,2] 1 / 3 \ 2 Output: [3,1,null,null,2] 3 / 1 \ 2 Example 2: Input: [3,1,4,null,null,2] 3 / \ 1 4 […]

## How to Ace Amazon Behavioral Interview

## Computer Networks

Computer Networks. Part One: LANs and WANs Computer Networks. Part Two: Network Hardware Computer Networks. Part Three: Ethernet Fundamentals Computer Networks. Part Four: LAN Topology Computer Networks. Part Five: Switched Ethernet LANs Computer Networks. Part Six: The TCP/IP Protocol Stack and Routers Domain Name System DNS

## Twos complement: Negative numbers in binary

Two’s Complement Representation of Negative Numbers

## Binary Left Shift << and Right Shift >>

Binary Left Shift << When shifting left, the most-significant bit is lost, and a 0 bit is inserted on the right end. Left shift is equivalent to multiplying the bit pattern by 2k (if we are shifting k bits). 10 << 2 = 10 * 22 = 10 * 4 = 40 10 << 3 = 10 […]

## Leetcode – 117. Populating Next Right Pointers in Each Node II

Given a binary tree struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL. Initially, all next pointers are set to NULL. Example: Input: {“$id”:”1″,”left”:{“$id”:”2″,”left”:{“$id”:”3″,”left”:null,”next”:null,”right”:null,”val”:4},”next”:null,”right”:{“$id”:”4″,”left”:null,”next”:null,”right”:null,”val”:5},”val”:2},”next”:null,”right”:{“$id”:”5″,”left”:null,”next”:null,”right”:{“$id”:”6″,”left”:null,”next”:null,”right”:null,”val”:7},”val”:3},”val”:1} Output: {“$id”:”1″,”left”:{“$id”:”2″,”left”:{“$id”:”3″,”left”:null,”next”:{“$id”:”4″,”left”:null,”next”:{“$id”:”5″,”left”:null,”next”:null,”right”:null,”val”:7},”right”:null,”val”:5},”right”:null,”val”:4},”next”:{“$id”:”6″,”left”:null,”next”:null,”right”:{“$ref”:”5″},”val”:3},”right”:{“$ref”:”4″},”val”:2},”next”:null,”right”:{“$ref”:”6″},”val”:1} Explanation: Given […]