abnayak/brainz

Interview Puzzles

Brainz (Programming puzzle, Common algorithms repository)

1. ProjectEuler: Contains solutions for projecteuler.net puzzles.
2. Leetcode: Solution to leetcode.com algorithm problems.
3. InterviewBits: Solution to inteviewbits.com puzzles.
4. Sorting: C++ implementation of few simple sorting algorithms.

Important Java methods and techniques to solve problems faster

1. Fill an array with a single value

   Arrays.fill(intArray,1);

2. Convert an array to linked list

   Integer[] arr = {1, 2, 3};
   List<Integer> list = new ArrayList<Integer>(Arrays.asList(arr));

   Notice arr of Integer array not int array

3. Print an array

   System.out.println(Arrays.asString(arr));

Must know data structure in java

1. List : ArrayList, LinkedList
2. HashTable
3. Stack
4. Deque: ArrayDeque, ConcurrentLinkedDeque, LinkedBlockingDeque, LinkedList

Iterating collection:

1. Iterate a HashMap
2. Iterate a PriorityQueue

Java Generics

1. Implement a QuickSort using the java API to sort a custom object.
2. Implement Heap data structure.
3. Difference between HashTable and HashMap.
4. Concrete implementation of interface collections.
5. Read the Collections APIs.

C++ Pair equivalent in Java

Pair is not natively supported in Java but we can use Map.Entry object to achieve the same objective.

Concrete implementations of Map.Entry.

1. AbstractMap.SimpleEntry<K,V>
2. AbstractMap.SimpleImmutableEntry<K,V>

Finding length/size of various Collection objects

1. Array: array.length
2. String: string.length()
3. Collection object(Stack, Queue, List): object.size()

String and character

• Convert a integer to character

  Character.forDigit(int_value, 10);

• Convert a String to character array

  string.toCharArray()

Reference examples

1. Combination sum
2. Search an element in rotated array

String problems

1. Multiply to strings (only containing number) to generate a string

Two Pointers

1. Count the number of possible triangles
2. Biggest rectangle in a histogram

Parenthesis Validation

BackTrack

1. https://www.interviewbit.com/problems/palindrome-partitioning/

Hashing

1. Find the length of the longest consecutive elements sequence in a given array

Integer conversions

String to int: Integer.parseInt("1"); Char to int: Character.getNumericValue('1'); int to String: Integer.toString(1);

Problem Collection

Find all unique combinations in an array where sum equals to a value https://leetcode.com/problems/combination-sum-ii/

Find subsets of set with unique elements https://www.interviewbit.com/problems/subset/

Find unique subsets with duplicates: https://www.interviewbit.com/problems/subsets-ii/

Find unique permutations with duplicates: https://www.interviewbit.com/problems/all-unique-permutations/

Find all the permutations of a set https://www.interviewbit.com/problems/permutations/

Find the largest continuous sequence in a array which sums to zero. https://www.interviewbit.com/problems/largest-continuous-sequence-zero-sum/

Dynamic Problem collection

Find Bitonic (first increasing then decreasing) subsequence in an Array https://www.geeksforgeeks.org/dynamic-programming-set-15-longest-bitonic-subsequence/