QA World Interview Questions and Answers

To check if a string can become a palindrome, count the frequency of each character. If there is at most one character with an odd frequency, it can be rearranged into a palindrome.

• Count the frequency of each character in the string

• Check if there is at most one character with an odd frequency

• If yes, the string can be rearranged into a palindrome

Given an array find if there are two elements are present that sum to target, else return -1

• Iterate through the array and for each element check if target - element is present in the array

• Use a hash table to store the elements and their indices for faster lookup

• If no such pair is found, return -1

Quick sort has worst case time complexity when the pivot element is either the smallest or largest element in the array.

• Pivot element is the smallest or largest element in the array

• Array is already sorted in ascending or descending order

• Pivot selection strategy is not efficient

Use two pointers, one moving twice as fast as the other, to find the middle element of a linked list in O(n) time complexity.

• Initialize two pointers, slow and fast, at the head of the linked list.

• Move the slow pointer one step at a time and the fast pointer two steps at a time.

• When the fast pointer reaches the end of the list, the slow pointer will be at the middle element.

Data structures are used in real life for organizing and managing data efficiently.

• Storing and retrieving contact information in a phone book using a hash table

• Organizing and searching for books in a library using a binary search tree

• Managing a playlist of songs using a linked list