ZPP

In complexity theory, ZPP (zero-error probabilistic polynomial time) is the complexity class of problems for which a probabilistic Turing machine exists with these properties: In other words, the algorithm is allowed to flip a truly-random coin while it is running. It always returns the correct answer. (Such an algorithm is called a Las Vegas algorithm.) For a problem of size n, there is some polynomial p(n) such that the average running time wil... more

In complexity theory, ZPP (zero-error probabilistic polynomial time) is the complexity class of problems for which a probabilistic Turing machine exists with these properties: In other words, the algorithm is allowed to flip a truly-random coin while it is running. It always returns the correct answer. (Such an algorithm is called a Las Vegas algorithm.) For a problem of size n, there is some polynomial p(n) such that the average running time will be less than p(n), even though it might occasionally be much longer. Alternatively, ZPP can be defined as the class of problems for which a probabilistic Turing machine exists with these properties: The two definitions are equivalent. The definition of ZPP is based on probabilistic Turing machines. Other complexity classes based on them include BPP and RP. The class BQP is based on another machine with randomness: the quantum computer. The class ZPP is exactly equal to the intersection of the classes RP and Co-RP. This is often taken to be... less