Find the n’th Node from the end of a given Linked List

Objective: Given a linked list and integer ‘n’, write an algorithm to find the nth node from the end in the Linked List.

Example:

Original List : ->1->2->8->3->7->0->4
Output : 3rd Element from the end is : 7

Input: An unsorted linked list and integer k

Output: The kth to Last Element of a Singly Linked List

Approach:

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Remove Duplicates from an Unsorted Linked list

Objective: Write a program to remove the duplicates from an unsorted linked list

Example:

Input Linked List : 1->2->2->4->3->3->2
Output : 1->2->4->3

Input: An unsorted linked list

Output: Linked list with no duplicates.

Approach:

  • Create a Hash Map
  • Take two pointers, prevNode and CurrNode.
  • PrevNode will point to the head of the linked list and currNode will point to the head.next.

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Check if one string is Rotation of another string

Objective: Write an algorithm to check if one string is Rotation of another string. This question has been asked in the Amazon interview.

Example:

Input Strings : 'sumitjain' and 'tjainsumi'
Output : true

Input String : 'Jaain' and 'ainJ'
Output: false

Input: Two Strings

Output: True or false based on whether strings are rotation of each other.

Approach:

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String Compression using count of repeated characters – Run Length Encoding

Objective: Write an algorithm to compress the given string by using the count of repeated characters and if new compressed string length is not smaller than the original string then return the original string.

Example:

Input String : ssssuuuummmmmmiiiittttttttttttt
Compressed String : s4u4m6i4t13

Input String : Jaain
Compressed String : Jaain (Since compressed string is length is greater than original string)

Input: A String

Output: either A compressed string or original string whichever us smaller.

Approach:

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Reverse a Linked List

Objective: Reverse the given linked list.

Input: A Linked List

Output: Reversed Linked List

Example:

Input : ->30->25->20->15->10->5

Reversed : ->5->10->15->20->25->30

NOTE : Click Reverse a Linked List – Part 2 to see the another implementation of this problem.

Approach:

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Find a pair of numbers from an array whose sum equals k

Objective: Write an algorithm to find out whether in a given array there exists or not two numbers whose sum is exactly equals to a given number. This problem has been asked in Amazon and Microsoft interviews.

Input: An array arrA[], A number k

Output: True or false based upon we have found any two numbers in array arrA[] whose sum is equal to k

Approach:

Method 1: Using Binary Search

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Check If String has All Unique Characters

Objective: Write an algorithm to find out whether in a given string contains all the unique characters. This question has been asked in the Amazon and Microsoft interviews.

Input:  A String

Output: True or false based upon whether string contains all the unique characters or not.

Approach:

Method 1.

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Find Whether Given String is palindrome or Not.

Objective : Write an algorithm to find Whether Given String is palindrome or Not.

Input:  A String,

Output: true or false on whether string is palindrome or not

Approach:

  • Use recursive approach
  • Compare first and last characters if they are not same- return false
  • If they are same make, remove the first and last characters and make a recursive call. 

Example:

Jain niaJ => compare ‘J’ with ‘J’ =>returns true

ain nia => compare ‘a’ with ‘a’ =>returns true

in ni => compare ‘i’ with ‘i’ =>returns true

n n => compare ‘n’ with ‘n’ =>returns true

string length <2 => returns true

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Find a peak element in a Given Array

Objective : In this article we will discuss an algorithm to Find a peak element in a Given Array. We will see the recursion techniques to solve this problem.

Peak Element: peak element is the element which is greater than or equal to both of its neighbors.

Input:  Array, arrA[] .

Output: A peak element and its index

Approach:

A simple approach is to do a linear scan to a array and using few variables we can find a peak element. But the Time Complexity will be O(n) but real question is, Can we do better?

The Answer is yes, by using Binary Search techniques.

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Find two Missing Numbers in a Sequence of Consecutive Numbers

Objective : Write an algorithm to find two Missing Numbers in a Sequence of Consecutive Numbers

Input:  Array, arrA[] with two missing numbers and Range

Output : Two missing numbers

Approach:

    • Approach is very simple, Add all the given numbers say S
    • Calculate sum of N numbers by formula n(n+1)/2 , say N
    • Find sum of two missing numbers a+b = N-S

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Find a Missing Number From a Sequence of Consecutive Numbers

Objective : You have been asked to Write an algorithm Find a Missing Number From a Sequence of Consecutive Numbers

Input:  Array, arrA[] with a missing number and Range

Output : missing number

Approach:

  • Approach is very simple, Add all the given numbers say S
  • Calculate sum of N numbers by formula n(n+1)/2 , say N
  • Find missing number m = N-S

Read moreFind a Missing Number From a Sequence of Consecutive Numbers