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

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.

When characters are not ASCII but could be anything alphabets or special characters

Valid or Well Formed Parentheses | Part – 1

Objective: You have been asked to write an algorithm to find Whether Given the Sequence of parentheses is well-formed. This question was asked in the Amazon Interview.

Input: A String contains a sequence of parentheses

Output: true or false on whether parentheses are well-formed or not

Approach:

• Idea is to have two counters, one for open parentheses ‘{‘ and one for close ‘}’
• Read one character at a time and increment one of the counters
• If any given point of time count of close parentheses is greater than the open one, return false
• If at the end both counters are equal, return true

Example: { { } { } } – Well-formed

{ { } { = Not well-formed

Code: