I received a call from HR at Expedia, who had seen my profile on LinkedIn. They asked a couple of simple questions, such as:

• What is a hashmap?
• How to find a combination of numbers in an array that add up to a certain value.

I had three rounds of telephonic interviews scheduled for a week or two later. Subsequently, I was asked to fly to Expedia in Gurgaon for three more interview rounds.

The questions were not difficult, and I was able to write code for all of them. However, based on the feedback, my code wasn't optimized enough.

Remove all characters of a string from another string. The algorithm should be less than O(m*n), where m and n are the lengths of the strings. The space used should be less than O(m+n).