## Permutation and Combination

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.. […]

## 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:

## 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 […]