Big O Notation with Absolute Value?

Question

I\'m going through some programming interview question books, and I\'ve seen reference to \"O(|A|)\" time complexity. I\'ve never seen this notation with the a

Answer 1

In set theory notation |A| is the cardinality of set A, in other words the number of elements contained in set A.

For Reference: http://www.mathsisfun.com/sets/symbols.html