Security hacker another crime such as destroying information contained in that system". These subgroups may also be defined by the legal status of their activities. A white hat hacker breaks security for non-malicious reasons, either to test their own security system, perform penetration tests, or vulnerability assessments for a client - or while working for a security company which makes security software. The term is generally synonymous with ethical hacker, and the EC-Council, among others, have developed certifications, courseware, classes, and online training covering the diverse arena of ethical hacking. A "black hat" hacker is a hacker who "violates computer security for
Prefix sum runs in linear time for integer keys that are smaller than the number of items, and is frequently used as part of radix sort, a fast algorithm for sorting integers that are less restricted in magnitude. List ranking, the problem of transforming a linked list into an array that represents the same sequence of items, can be viewed as computing a prefix sum on the sequence 1, 1, 1, ... and then mapping each item to the array position given by its prefix sum value; by combining list ranking, prefix sums, and Euler tours, many important problems on trees may