Killer Problems

1. Quick sort - Inplace partition
2. AtoI and ItoA conversion
3. Base conversion problems
4. Verify if all the characters in a given string are unique or not
5. Remove all the duplicates in a given string - Linked HashSet
6. insertion Sort 
7. Merge Sort
8. Binary Search - recursive and non-recursive
9. Stack - Datastructure - PUSH, POP, PEEK
10. Queues - DataStructure - INSERT, REMOVE, ...
11. Circular Queues - "
12. LInked Lists SLL
13. Linked Lists DLL
14. Linked List XOR based LL
15.  Concatenate two linked lists
16. Reverse a SLL
17. Reverse a DLL
18. Circular SLL
19. Lowest Common ancestor if an any given two nodes
20. 2 sorted arrays of non-repeating integers. Find min(abs(x-y))
21. Maximum value of continours sub sequence Kadane Algorithm
22. Given repeated sorted array and a number, Tell its first and last idex 
23. Reverse the words in a given sentence
24. Find an element in rotated binary sorted array
25. Find an element that is repeated more than n/2 times
26. Implement power function (a)b
27. Check if a given linked list is cyclic or not
28. Find a pair in an array that sum up to a number 
29. Reverse a pair of nodes in a SLL
30. Seggregate odd/even number of nodes in a given Linked list
31. Find the middle of a SLL
32. Addition of 2 linked lists
33. XOR based linked list - Insert, delete and display
34. Convert SLL to DLL
35. Circular shift an array of size n
36. Find the minimum element in a rotated sorted array
37. Pattern Matching - Rabin Karp Algorithm
38. K-way merge sort
39. Maximum Depth or Height a a given tree
40. Find all the subsets of a given set of integers 
41. Find the inorder successor a given node in BST
42. Heapsort
43. Find the minimum length of unsorted subarray to make whole array as sortd
44. Suffix arrays
45. Print all the permutations of a given stirng
46. Rearrange a stirng such that all the same characters be 'd' distant away
47. Rat in a Maze 0,0 to 7,7 ?
48. Find all the subset of elements in a given set whose sum equal to a target
49. Find if there is a subarray with sum 0
50. Find the median of given two input sorted arrays
51. Find the fixe dpoint a[3]=3 or a[1]=1 in a given sorted arary
52. Count # of key occurrences of a number in sorted array
53. Check if a given number is a multiple of 3 or not
54. Check if a number 'n' is power of 2 or not
55. Function to multiply n by 7
56. Multiply 2 numbers without * operator
57. Generate all prime numbers smaller than equal to n [Sieve of Erathosenes]
58. Make a fair coin from unbiased coin
59. Print all the possible words from phone digits 
60. Shuffle a given array / Randomize a given array of integers - Fisher Yates 
61. Reservior sampling - Select 'k' random elements from a stream with k/n probability
62. Given a number 'n'. Generate a Pascal Triangle
63. Generate all prime factors of a given number ;n;
64. Random number generator in arbitrary probability Distribution function
65. Check if a given number is fibonacci number or not
66. Longest common Subsequence
67. Minimum cost path, Find the cost of traversing from 0.0 to m,n
68. Coing change problem
69. Binomial  co-efficient via Pascal Triangle ?
70. Knapsack problem
71. Egg drop problem
72. Longest palindromic subsequence
73. Palindrome Partitioning. Determine minumum number of cuts to make substrings as palindromes
74. Partitioning problem - Two sets with equal sum
75. Maximum length chain of pairs
76. Check if a given linked list is a palindrome or not [stack or reverse]
77. Given a post order + Inorder array, Check whether array is BST or not
78. Array with bits 0110101101, flip them such that it has max number of 1's in it
79. Implement sizeof() operator
80. Find inorder successor of a BST
81. Find all the triangle triplets in an array
82. Josephus problem
83. Given a sorted skewed binary tree, createa a BST out of it
84. Return all elements in an array that are repeated twice only
85. Given an array, put all even numbers to left of array and odd numbers to right of array
86. Height of a given tree
87. Diameter of a given binary tree
88. Serialize/Deserialize a given binary tree
89. Find the just single repeated element in a a given array
90. Implement diff command in linux
91. Program to count number of 1's in a given number
92. Convert BST to DLL
93. Swap variables withour a temp
94. check if a number is prime or not
95. GCD of 2 numbers - Euclidean Algorithm
96. Median of a stream of numbers continous
97.  Print all the paths of a given binary tree from root to leaf
98. Modify/Relocate an array such that a[i] = a[a[i]]
99. Find a missing number in 4 Billion Numbers
100. Given 'n', Generate all valid paranthesis string of length 2n
101. Rectangle intersection problem - Find if rectangles overlap and area of rectangles
102. Dutch National Flag Problem 0-1-2
103. Increment an arbitrary precision integer, Stored in an array
104. Advancing through an array to reach end
105. Delete duplicates from a sorted array
106. buy and sell a stock once
107. buy and sell a stock multiple times
108. permute all the elemtns of an array
109. Compute next permutation represented 'n' as in an array
110. Random Sampling 
111. Sample online data 
112. Sudoku Checker Problem [Backtracking]
113. Sudoku Checker Problem - validate if its a correct sudoku
114. Base Conversion n(b1) to n(b2)
115. Given a column number, Find the corresponding column name in a excel spreadsheet
116. Char replacement in a string, Replace 'a' with 'dd', Remove 'b'
117. Validate if a given sentence is a palindrome or not
118. Look and Say Sequence, Given n, output nth number in the sequence
119. convert form roman numeral to decimal number
120. compute all the valid IP addresses
121. write a string sinusoidally - since wave fashion
122. Implement a runlength encoding algorithm
123. Merge 2 sorted linekd lists
124. Reverse a sublist of a given linked lists
125. Verify if a given tree is height balanced or not
126. Total # of nodes on longest path between 2 leaves in a tree, AKA Diameter of a given tree
127. Sum root-to-leaf paths in a binary tree
128. Given a BT, Return true if it has root-to-leaf path sum adding up to all values along the path equal to a given number
129. Implement inorder traversal without recursion - Morris Traversal
130. Implement inorder traversal with a stack
131. Iterative pre-order traversal
132. Iterative post-order traversal
133. Compute value of kth smallest node in a binary tree
134. Reconstruct a binary tree from a given traversal data (inorder + Pre or Post)
135. Construct a DLL from leaves of a binary tree
136. Print boundary of a given binary tree
137. Priority queues using Heaps 
138. Convert Minheap to Max heap
139. check if a given binary tree is a heap or not
140. Check if a given BT is complete or not
141. Check if a given array represents max heap or not
142. Given a infinite stream, Find the kth largest element at any point of time
143. Merge 'k' sorted arrays - external Sorting
144. Ternary search 
145. Level order traversal of a binary tree
146. Heap - Insertion, Deletion to max heap - Priority Queues
147. Verify if 2 strings are anagrams or not
148. Longest increasing sub sequence
149. Given 2 string and operations (insert, delete and replace) can be done on str1, Find the minimum number of edits required to convert str1 to str2
150. Rod cutting, Max value obatined by cutting rod of 'n' length  + Price and values are considered
151. Maximum sum increasing subsequence
152. Longest biotonic subsequence
153. Floyd Warshall Alogorithm
154. Minimum number of jumps required to reach end 
155. Pattern searching - KMP Knuthh Morris Pattern Algo
156. Given n+2, find the 2 repeated elements from 0 to n 
157. Lowest common ancestor in a BST
158. Find inorder predecessor and successor in a BST
159. Delete a node in BST - 3 cases
160. merge two BSTs with limited extra space
161. Find ceil and floor value of a given key in a BST
162. Binary trees - Full, complete, Perferct, balanced ?
163. Size of a binary tree
164. Convert a Binary tree in to its mirror tree Inplace post order
165. Count # of leaf nodes in a binary tree
166. Check for childrem sum property in a given binary tree
167. maximum width of binary tree - i.e find a level that contains maximum number of nodes
168. Check if a tree is foldable or not
169. Print all the nodes with distance 'k' apart from the root
170. Get level of a node in a binary tree
171. Print ancestors of a given node in binary tree
172. Check if a binary tree is a subtree of another binary tree
173. Connect nodes at same level in a binary tree - extended level order
174. Populate inorder successor nodes of all nodes in a binary tree - Reverse inorder
175. Convert given tree to its sum tree 
176. Find the maximum sum from root to leaf in a BT
177. Print the boundary of a BT
178.  Construct a Full BT form given pre-order & post order. There are other possible combinations of traversals too
179. Iterative post-order traversal using stacks
180. Reverse level order traversal 2 stacks 
181. Count BST nodes that lie in a given range low, high
182. Clone a linkedlist with next and random pointer
183. Wildcard pattern matching . ? *
184. Implement a stack using  queues 
185. Implement a queue using stacks
186. generate a random number in a range
187. Select a random node in a given SLL
188. Check if a number is a palindrome or not
189. Existenece of increasing triplet in a sequence
190. Sum of all the numbers that are formed from root to leaf path
191. Find all the possible words in a given word boggle. you can assume a routine being provided to check if a word exists in a dictionary or not
192. Longest path in a given matrix
193. Find the peak element in an given array 
194. Four array sum problem a[i] + b[j] + c[k] + d[l] whose sum is zero
195. Verify if string 't' is a subsequence of another string 's'
196. Remove duplicates from sorted arrays. how about if we allow max number of duplicate elements
197. Submatrix sum queries. Given (r1,c1) and (r2,c2)
198. Four sum problem such that a+b+c+d = target 
199. Partition a given linked list with values across 'x'
200. Find the sum of all digits in a number recursively until it becomes a single digit
201. Longest continuous/consecutive sub sequence - DP
202. Implement a trie/prefix trees
203. Sort a hashMap<k,v> based on values
204. Sort the elements based on frequence Ex: tree -> eetr
205.  sum of two number without +,-,*,/
206. Repeated DNA subsequence maxlength =10, AGCT 
207. Flight Drone Fuel 
208. A product array puzzle, a[i] = prod(0-i-1 & r+1 to n)
209. Word count engine, Given a doc - count number of words
210. Count number of possible triangles in a given array
211. Find the # of leaders in a given array
212. Find the sub array continous sum equal to a target
213. Find the equilibrium index of a given interger array
214. Minimum number of paltforms required for a railway station given the arrival and departure of the trains
215. Find the maximum of all subarrays of size k
216. Find the kth smallest or kth largest element in a given array
217. Trapping Rain Water - Find the max amount of water that can be stroed in a given hieght of bridges repesented as an array
218. Chocolate distribtuion problem - Find the minimum difference such tath every m student gets a packet and the diff of min and max packet received by a student is minimal
219. Find an elemtn with all left side smaller and all right side elements are greater
220. Convert a givne unsorted array in to zig zag fashion [a>b<c>d<e>f...]
221. Relative Sorting - Sort an array according to the order defined by another array
222. Traverse the matrix in a sprial way
223. Arrange the given numbers in an array to form the biggest number
224. Largest sub array with equal number of 0s and 1s
225. Check if a string has valid set an order of paranthesis
226. Largest palindrome in a given string
227. Recursively remove all the adjacent duplicates characters progressively - azxxzy
228. Check if a given string is rotated by two places
229. Find the longest common substring in given two strings
230. Given a string, Find the minimum # of characters to be inserted to convert to a plindrome
231. Find the longest substring with all distinct characters
232. Implement a string indexOf method
233. Given an array of String, Find the longest common prefix
234. Given an unsorted array. Find the continous subarray that adds upto a target
235. A special linked list with next and random pointer with each list sorted, Flatten it in sorted order
236. Find the intersection point or merge point in the linkedlist
237. Find the next largest element to right of the array
238. Get the minimum element from  a stack at any given point of time 't'
239. Given (capacity, distance), Find a starting point to circle the tour
240. Given infinity stream, Find the first non-repeating character
241. Print the left view of Binary tree
242. Print bottom view of binary tree
243. Print right view of binary tree
244. Print vertical order of binary tree
245. Print level order of a tree traversal in spiral form
246. Print level order of a tree in reversal form
247. Given a binary tree in which each node contains a number, Find the max possible sum from one leaf node to another leaf node
248. Find the median in a infinite stream of interegers
249. Given a string repated characters, the task is to rearrange the chanracters in a string such that no two adjacent characters are same
250. Given a 2D screen, location of a pixek in a screen and  a color k, Repalce all such pixels with color 'y'
251. Count all possible paths from top left to right bottom. i,e 0,0 to m,n only right n down directions are allowed
252. Given an integer array and a target N , Find all the unique combinations in A where sum is equal to target. element can be used only once.
253. Same as above question, but what if element can be used any nnumber of times
254. Given n of keystorkes allowed, Find the max A's that can be printed if permissible keystrokes are - ctrl+A, ctrl+c, ctrl+v and A
255. Find the largest subarray with 0 sum
256. Given two array of integers,  Find the two arrays sum be equal of swapping atmost one integer ?
257. Given an array of integers, and window 'k' , Print the count of distinct numbers in all windows of size k
258. GIA (Given Integer array), Find if an array can be divided in to pairs such that sum of every pair is divisible by 'k'
259. GIA, Find the length of longest consecutive subsequence
260. Find if one integer array is subset of another array
261. Given two unsorted arrays, Find all the pairs from both arrays where sum is equal to x
262. Find the first repeated character in a given string s
263. GIA, Print the total count of subarrays with their sum equal to 0
264. Given a string and pattern, Find the character in a string that is present at minimum index in a second string.
265. Find the uncommon character of two string . A uncommon character is something i.e present in one string or other but not both
266. Find the smallest window in a string that contains all characters in another string
267. GIA, Find the first element that occurs k number of times
268. Given a string, Check if its possible to remove atmot one character such that frequencies of all characters of each distinct chracter becoms same in a string
269. Depth first traversal of a graph
270. Breadth First Traversal of a graph
271. Detect a cycle in a directed graph
272. Given set of vertices and edges, Sort them in a topological order
273. Find the number of islands in a given 0/1 matrix
274. Find the shortest distance from source to all destination vertices [Djikstra]
275. Find the minimum number of swaps required to sort an integer array
276. Given a graph with n nodes and m edges, Find the total number of strongly connected components
277. Given a binary 0/1 matrix, Find the shortest path that exists from a given source to destination cell (LEE algorithm)
278. Given n*n matrix with 0,1,2,3. Find whether a path exists from source 1 to destination 2 via cell 3. 0 - means blocked
279. Circle of Strings, Given a list of strings, Find whether we can form a circle from start and last character ?
280. Find the minimum number of jumps required to reach end
281. Find the # of ways to make a change for N cents if infinite supply of coins exist
282. Find the minimum  coins required to make change for N cents on infinite supply of coins
283. Partition Problem - Find if an array can be partitioned into two subsets such that their sum is equal
284. Sort Stack the boxes of N types. Each box has l,d and h. Create a stack of boxes as tall as possible. You can rotate the boxes if needed
285. Find the longest path in the matrix such that all cells along the path are in increasing order with a difference of 1
286. same as above but just with increasing path without constraint of diff 1
287. Find an element that appears only once in sorted order
288. Find kth element in two sorted arrays
289. Find the last index of '1' , Given an array of 0s and 1s
290. Find the first set bit in an integer
291. Given two integers, Find the right most different bit
292. Given an integer, Find if kth bit is set from right or not
293. Check if a given integer is power of 2 or not
294. Given 2 integers, Find the # of bits differ in each integer
295. Find the total number os longest consecutive 1's in an integer
296. Find the most frequesnt word in a given list or array of strings
297. Find the median of two sorted arrays
298. Given an array, find the maximum (j-i) such that a[j] >= a[i]
299. Given a sentence, Output a string by dropping a seen character alternatively.
300. Find if one can reach end of the array assuming a[i] being the number of cells to jump
301. Print all the elements in a sorted from a row and columnwise sorted matrix
302. Search an element in a row and column wise sorted matrix
303. Regular Expression - Search for a pattern with ? * in the text
304. Delete a node in the middle of single linked list. Only a pointer to middle node is given
305. Find the three closest elements from a given three sorted arrays such that a[i]-b[j], b[j]-c[k], c[k]-a[i] is minimum
306. Find the largest rectangular histogram
307. Maximum size square of submatrix that has all 1's
308. Find all the triplets with 0 sum in an array
309. Max product sub array
310. Sliding Window Maximum, Find the max of 'k' in window
311. Largest submatrix sum of size k
312. Word Boggle - Given a 2D char matrix, Find if the word exists in a given grid.
313. Word Boggle 2 - Given a dictionary of words, Return all the words that exist in  a grid
314. Word Break - Given a dictionary of words and a concatenated string, Ensure if you can segement the concat string based on dictionary words
315. Merge all the overlapping interval pairs
316. Given 2 sorted lists, merge in to single list by merging intervals
317. Count the number of ways to reach n stairs
318. Find the closest leaf node in a Binary tree
319. Add bold tag in the string
320. Merge two binary trees
321. Find the closest time given HH:MM
322. Reverse an integer
323. Find the largest value in a tree at each level
324. Find the # of ways of climbing steps to top . Max of 1-2 stops each time
325. Find palindrome pairs in a given list of words
326. Word Square - Find the word [row, column] of fixed length
327. Set Matrix Zeros - Replace a row and its respective column to 0
328. Find the median of 'k' elements of sliding window
329. Word Ladder Problem. Find the minimum traversals in a dictionary to reach target
330. Find the longest valid parentheses in a given string
331. Given an integer, Find the possible ways to decode it. a-1, b-2...z-26
332. Clone a undirected graph
333. Implement calculator - Given a expression string
334. Implement a program to version matching. major.minor.subminor
335. Implement Tic Tac Toe Game
336. Design and Implement a hit counter
337. Implement a BST Iterator - hasNext and next
338. Implement a array iterator - hasnext and next
339. Implement a list of list iterator - hasnext and next and remove methods
340. Palindrome Partitioning - Find the minimum number of cuts required to make a string palindrome substrings
341. Convert an integer to words - similar to how you write in check leaf