• Find even or odd
• Count digits in a number
• Reverse a number
• Prime number
• Armstrong number
• Check palindrome of number
• Square root of a number
• Find last digit in a number
• Find power of a number
• GCD
• Print all divisors of a number
• Perfect number

Basics with traversal

• Find the maximum and minimum element in array
• Sort an array of 0s , 1s and 2s
• Check if two arrays are equal or not
• Array subset of another array
• What is an array? How is it represented?
• Find third largest element in array
• Find missing number in array
• Find repeating number in array
• Rotate the array by 1
• Search an element in array
• Count frequency of elements in array
• Rotate the array by k
• Learn what is map and how its represented before moving forward

Two pointer

• Union of two arrays
• Remove duplicates from array
• kth element of 2 sorted arrays
• Find pair with given sum
• 3 Sum
• 4 Sum
• Find triplets with zero sum
• Find count of triplets
• Intersection of two arrays
• Length of longest subarray with sum k
• Trapping rain water

Advanced Problems

• Majority element
• Count inversions
• Merge intervals
• Kadane's algo (super imp)
• Maximum product subarray
• Next permutation
• Seive of eratosthenes (Popular algo for prime numbers)

• Maximum num of 1's row
• Left rotate matrix k times
• What is a 2D Array? How to access element?
• Search in a matrix
• Rotate by 90 degree
• Print matrix in diagonal pattern
• Set matrix zeros

Basic pattern

• Find floor and ceil in sorted array
• Find first and last occurrence of element in sorted array
• Find missing num from 1 to N
• Find square root
• Search for element in infinite array
• Search in a sorted array

Sorted rotated array

• Search element in sorted rotated array
• Number of times array is sorted
• Minimum element in sorted rotated array
• Maximum element in sorted rotated array

Biotonic array

• Find the peak element
• Search element in biotonic array

Matrix

• Find row with maximum number of 1s
• Search in row wise column wise sorted matrix
• Search in sorted matrix II
• Find peak in sorted matrix

Application(Super imp)

• Allocate minimum pages
• Painter partition
• Split array largest sum
• Minimum num of days to make m bouquets
• Capacity to ship packages within D days
• koko eating bananas
• kth smallest number in matrix multiplication table
• kth smallest pair distance
• Ugly number II
• Median of 2 sorted arrays
• Find smallest divisor given threshold
• Aggressive cows

• Selection sort
• Insertion sort
• Merge sort
• Quick sort
• Bubble sort

Basic patterns

• Union and Intersection of LL
• Delete without head pointer
• Create, Insert, Delete Operations in LL
• Search for an element in LL
• Reverse a LL
• Check if LL is a Palindrome
• Middle element of LL
• Find the intersection point of Y LL
• Count pairs with given sum
• Reverse LL in groups of given size

Loop

• Find length of loop in LL
• Find the starting point of loop
• Remove the loop
• Detect loop in LL

Sorting, Merging & Related

• Sort 0s, 1s, 2s in LL
• Pairwise swap elements
• Merge sort in LL
• Quick sort in LL
• Remove occurrence of duplicates in sorted & unsorted LL
• Seggregate even and odd nodes in LL
• Merge k sorted LL

Arithmetic(Reversal & traversal - Once you learnt these, you can solve probs in this pattern)

• Add 2 numbers represented as LL
• Add 1 to a number represented as LL
• Subtraction on LL

Must solve other probs(Try to solve these probs on own, brute force atleast you can come up for most of them after solving above)

• Learn the basics of circular LL
• Rotate LL
• Delete nodes having greater value on right
• Delete N nodes after M nodes
• Clone a LL
• Length of longest palindrome in LL
• Flattening a LL
• Delete all occurrence of node

Double Linked List

• Insert, Delete, Reverse DLL
• Pairs with given sum in DLL
• Learn the basic representation of the nodes in LL

Basic

• Implement 2 stack using array
• Check for balanced parenthesis
• What is stack? Learn how to represent the data structure and working of it
• Get min from stack in O(1) space and time

Next greater element

• Next greater element
• Next greater element II

Next smallest element(Once above pattern is covered, try to solve this on own)

• Next smallest element on left
• Next smallest element on right
• Trapping rainwater
• Stock span problem
• Maximum rectangular area on histogram
• Max rectangle

Expressions

• Infix to postfix
• Evaluation of postfix expression
• Prefix to postfix
• Arithmetic expression evaluation

Reversing stack

• Insert at bottom of stack
• Reverse a stack
• Sort stack

Implementation probs

• Celebrity problem
• Restrictive candy crush
• Count the reversals

Basic pattern

• What is queue? Learn the basic representation and how its implemented?
• Implement queue using stack(super imp)
• Implement stack using queue(super imp)
• Implement queue using linkedlist
• Reverse a queue

Implementation probs

• Circular tour
• First non repeating char in stream
• Reverse first k elements in queue
• LRU Cache(super imp)
• Nearly sorted
• Minimum cost of ropes

Traversals

• PreOrder Traversal
• InOrder Traversal
• PostOrder Traversal
• Level Order Traversal
• Understand the basic of how tree data structure is represented
• Boundary Traversal
• Vertical Traversal
• Top View of BT
• Bottom View of BT
• Left View of BT
• Right View of BT
• Diagonal Traversal

Basic and Easy patterns(Try to solve these once you learnt traversals)

• Height of the tree
• Diameter of the tree
• Check if 2 trees are identical
• Check if subtree
• Check for balanced tree
• Lowest common Ancestor in BT
• Symmetric tree
• Mirror of a tree
• Check if isomorphic
• Insert node in a tree
• Sum tree

Path and Distance

• Root to leaf paths
• Nodes at given distance
• Root to leaf path sum
• Maximum path sum from any node
• K Sum Paths
• Range sum of BST
• Minimum distance between 2 nodes
• Maximum distance between node and ancestor
• Min time to burn a tree

Binary Search Tree

• Understand what BST is?
• Insert a node in BST
• Count BST nodes in the given range
• Lowest Common Ancestor in BST
• Inorder successor and predecessor
• BST to greater sum tree
• Delete given node from BST
• Search a value in BST
• Find minimum and maximum in BST
• Find the Kth largest element/kth Smallest in BST
• Check for BST
• Find the closest element in BST
• Largest BST in BT
• Merge two BST
• Populate inorder successor for all nodes

Construct from given

• Construct Binary Tree from Preorder and Inorder Traversal
• Construct BT from parent array
• Construct Binary Tree from Inorder and Postorder Traversal
• Construct BST from given preorder traversal

Subtree & Other must do tree probs

• Serialize and deserialize BT
• Maximum sum of non adjacent nodes
• Duplicate subtree
• Flatten BT to linked list
• Largest subtree sum in a tree

Fixed Sliding Window

• Maximum sum subarray of size k
• Maximum of all subarray of size k
• Count substring of length k with k-1 distinct elements
• Maximum of minimum for every window
• Count distinct element in every window
• First negative integer in every window of size k

Variable Sliding Window

• Subarray with given sum
• Subarray with 0 sum
• Smallest window of distinct elements
• Smallest window containing 0,1,2
• Smallest window in string containing all chars of another string
• Length of longest substring
• Largest subarray of 0s and 1s
• Count of anagram occurrence
• Max consecutive ones III
• Count number of nice subarrays
• Longest repeating char replacement
• Minimum window substring
• Subarray with k diff integers
• Longest subarray with given sum k
• Fruit into basket
• Minimum window subsequence
• Sliding window median

Traversals & Basic

• Understand how graph is represented?
• Detect cycle in Directed graph
• Detect cycle in Undirected graph
• BFS Traversal
• DFS Traversal
• Detect Negative cycle in graph

Connected component(After traversal, this will be easy to solve)

• Number of Islands
• Number of distinct island
• Number of closed island
• Connected component
• Number of Provinces

Bipartite

• Bipartite graph
• M-colouring

Shortest Path

• Find shortest path in DAG
• Djikstra Algo
• Step by Knight
• Find if path exists
• Minimum cost path
• Word ladder I
• Word ladder II
• Floyd warshal algo
• Find shortest path in UG
• Shortest path source to destiny
• Covid spread
• Bellmanford algo

• Possible words from phone digits
• Subsets
• Permutation with spaces
• Generate parantheses
• Generate IP address
• Solve the sudoku
• kth permutation
• Word search
• Palindrome partition of string
• Decode the string
• Letter case permutation
• sum string
• word boggle
• Largest number in k swaps
• Partition array to k subsets
• Understand the basics of backtracking and start solving
• Permutation II
• Permutations of a string
• Combination sum I
• Combination sum II
• Combination sum III
• Rat in maze
• Unique subset
• N-Queen
• N Queen II

• Minimum number of jumps
• Activity selection prob
• N meetings in a room
• Minimum platforms
• Job sequencing prob
• Fractional knapsack
• Jump game
• Insert interval
• Minimum cost of ropes
• Valid parantheses - Minimum
• Least recently used
• Non overlapping interval
• Minimum operations
• Minimize the sum of product
• Largest number possible
• Lemonade change
• Minimize the height
• Minimum number of coins using greedy
• Merge interval
• Partition labels
• Cinema seat allocation
• Max length chain
• Shortest job first

Basic

• Understand the basics!!

1D - Linear DP

• Count way to reach nth stair
• Count way to reach nth stair
• House robber II
• Count num of hops
• House robber

2D Grid DP

• Count paths - grid
• Unique paths II
• Minimum path sum in grid
• Minimum path sum in triangular grid
• Minimum/Maximum falling path sum
• Count all possible paths with condition
• Max path sum
• Number of paths with k coins
• Minimum falling path sum II

DP on subsequence

• Coin change
• Min number of coins
• Rod cutting
• Target sum
• Knapsack with duplication items
• Partition equal subset sum
• Minimum cost to fill given weight in bag
• Subset sum problem
• Count subset with given sum k
• Minimum sum partition
• Count partition with given diff
• 0-1 Knapsack
• Maximum non adjacent subsequence

DP on Increasing subsequence

• Longest increasing subsequence
• Print longest increasing subsequence
• Longest string chain
• Num of longest increasing subsequence
• Longest bitonic subsequence
• Longest divisible subset

DP on strings

• Longest palindromic subsequence
• Form a palindrome with minimum insertions
• Min num of deletions and insertions to make string s1 equal to s2
• Shortest common supersequence
• Longest common substring/subarray
• Longest palindromic substring
• Longest repeating subsequence
• Longest common subsequence
• Print Longest common subsequence

DP on string

• Distinct occurence
• Wildcard pattern matching
• Longest valid parentheses
• Word break
• Word wrap
• Interleaved strings
• Edit distance
• Word break II

DP on stocks

• Best time to buy and sell stock
• Best time to buy and sell stock III
• Best time to buy and sell stock IV
• Best time to buy and sell stock with cooldown
• Best time to buy and sell stock with transaction fee
• Best time to buy and sell stock II

DP on partition and MCM

• Minimum cost to cut stick
• Burst balloons
• Boolean Parenthesization
• Palindrom partitioning
• Partition array for max sum
• Max rectangles area with all 1s
• Count square submatrices
• Matrix chain multiplication

Basic patterns

• What is heap? Understand the data structure
• Min heap implementation
• Max heap implementation
• Convert min heap to max heap

Top k pattern

• kth largest in array
• kth smallest in array
• Top k frequent elements
• Top k frequent words
• Frequency sort
• kth largest num in streams
• Reorganize string
• Reorganize string k distance apart
• kth smallest sum of matrix
• ugly num II

Merge k sorted pattern

• Merge k sorted array
• k pairs with smallest sum
• k smallest nums in M sorted list

Two heaps pattern

• Find median from data stream
• Sliding window median
• Maximum capital/IPO

Minimum number pattern

• Minimum cost to connect ropes
• Meeting room II
• Minimum cost to hire k workers
• Minimum num of refueling stops
• Minimum num of CPU

• Implement trie
• Search suggestions system
• Replace words
• Design add and search words
• Word search II
• Stream of characters

• Implement Atoi
• Minimum bracket reversals
• Remove all adjacent duplicates
• Hashing in strings
• Print all anagrams
• Z - Function
• Shortest palindrome
• Circle of strings
• Roman numerals to decimals
• KMP algo
• Count and say
• Rabin karp algo
• Boyer moor algo
• Longest happy prefix