I have been working on RTOS and Linux driver development for quite some time. Now I am interviewing at semiconductor companies and failing to answer questions about algorithms on strings, and time and space complexity. I have not studied discrete maths and algorithms during my as I have an electronics background.
How can I overcome this gap?
Introduction to Algorithms is a great algorithms book (and also happens to be listed 6th on the great influential book question)
Start with something simple like: Algorithms in a Nutshell (good starting point for interview like questions)
Or Algorithms For Interviews When you feel you know the above book, then you can think of diving into introduction to Algorithms.
You need to review most of the course material for a Data Structures and Algorithms class. In order to answer those types of interview questions, you don't generally need the material covered in Discrete Math.
If you want to take the long way around (and actually understand the topic), I recommend you actually work through the class material and listen to the lectures. Since UC Berkeley posts some of their lectures online, you can watch just such a class (with an excellent instructor) here:
http://webcast.berkeley.edu/course_details.php?seriesid=1906978343
Pay particular attention to the lectures on Big O notation, and the sorting and searching algorithms. Those tend to be the bits that people ask about for job interviews.
If you can't be bothered to actually spend the 30 hours watching the lectures and many more working through the problems, you should at least consult the book that course uses:
Goodrich and Tamassia's Data Structures and Algorithms in Java
I would suggest you Introduction to Algorithms(by CLRS) and Algorithm design manual for algorithms and complexity(by steven skienna) for understanding the Algorithms and complexity.Other than that there are quite a few good tutorials on algorithms and complexity at top coder ( site : topcoder.com/tc ) , you can check them out too.