When a tree is used there is a high chance that an index is used. The simplest type of index is a sorted list of key fields. A tree normally has a defined structure. In the case of a binary tree, you can use a binary search to locate any item without having to look at every item.
The tree data type is a type of graph meaning that many algorithms made to traverse a graph also work with a tree however, the algorithms can be much similar and must have a dedicated start node, that is the node with no other nodes linking to it.
The problem with a simple ordered list occurs when you start adding new items and have to keep the list sorted - it can be done reasonably efficiently but requires some modifications. Additionally, a linear index is not easy to share because the whole index needs to be “locked” when one user edits it, whereas one “branch” of a tree can be locked, leaving the other branches editable by other users (as they cannot be affected).
A hash table is an array where each index points to a linked list based on a hash value. A hash value is a value determined by a hash function. A hash function determines a unique value based on the data it is storing. This allows for access of data in constant time because the computer always knows where to look.
Alex Lifeson
Alex Lifeson, OC (born Aleksandar Živojinović; August 27, 1953) is a Canadian musician. He is best known as the guitarist and co-founder for the Canadian rock band Rush. Lifeson has been a member of the band since 1968.
In Rush, Lifeson plays electric and acoustic guitars. He also plays other instruments including: mandola, mandolin and bouzouki.
Along with his music career, Lifeson is part owner of a Toronto restaurant called "The Orbit Room." He is also a licensed airplane pilot.
Hepatitis C
Hepatitis C is an infection that mostly affects the liver. The hepatitis C virus (HCV) causes this disease. Often, a person with Hepatitis C does not have any symptoms (health problems or signs that he has the disease). However, chronic infection can scar the liver. Many years of infection may cause cirrhosis. Sometimes, people with cirrhosis also have liver failure or liver cancer. They can also have very swollen veins of the esophagus and stomach. The blood loss from this problem can kill.
Hepatitis C is usually spread by blood-to-blood contact (when blood from a person with Hepatitis C contacts (touches or gets into) another person's bloodstream). The most common ways that this happens are through intravenous drug use (when a person shoots drugs into one of their veins, with a needle that was already used by a person infected with Hepatitis C); nonsterile medical equipment (medical tools that were not cleaned well enough after being used on an infected person); and blood transfusions (when a person is given blood that came from an infected person).
Around the world, about 130–170 million people have Hepatitis C. Scientists began studying the Hepatitis C virus in the 1970s, and in 1989 they proved that the virus exists. As far as scientists know, this virus does not cause disease in any animals other than humans.
The medications that are normally used to treat Hepatitis C are called peginterferon and ribavirin. Between 50-80% of people who are treated (or 5 to 8 out of every 10) are cured. However, if a person's Hepatitis C has progressed (or gotten worse) so much that the person has cirrhosis or liver cancer, the person might need a liver transplant (they might need to have surgery where they are given another person's liver, or part of another person's liver). This makes it possible for the person to survive, but the Hepatitis C virus usually comes back after the transplant. There is no vaccine that works to prevent people from getting Hepatitis C.
Hepatitis C causes acute symptoms (symptoms that begin quickly or last only a short time) in just 15% of people with the disease. More often, infected people have symptoms that are mild (not serious) and vague (not very specific), like a decreased appetite (not feeling like eating), fatigue (feeling tired), nausea (feeling like throwing up), pain in the muscles or joints, and losing weight. Every once in a while, an infected person may get jaundice (where a person's skin turns yellow, a sign that their liver is not working quite right). If it is not treated, Hepatitis C goes away by itself in 10-50% of infected people (1 to 5 out of every 10). This happens more often in young women than in other infected people.
Eighty percent (or 8 out of every 10) of people exposed to the Hepatitis C virus get a chronic infection (one that does not get better and lasts for a long time). Most experience very few or no symptoms during the first decades of the infection, although chronic Hepatitis C can cause fatigue (feeling tired). But in people who have been infected for many years, Hepatitis C can cause serious problems, like cirrhosis and liver cancer. Hepatitis C leads to cirrhosis in 10–30% (between 10 and 30 out of every 100) of people who have been infected over 30 years. People with Hepatitis C are more likely to get cirrhosis if they are men; if they are alcoholics; or if they also have Hepatitis B or HIV. Cirrhosis can cause serious problems on its own, but it also makes people more likely to get other serious illnesses. For example, people who get cirrhosis are twenty times more likely to get liver cancer (with about 1-3% getting liver cancer every year). People with Hepatitis C who are alcoholics are even more likely - 100 times more likely - to get liver cancer. Among people in general, 27% of all cases of cirrhosis, and 25% of all cases of liver cancer, are caused by Hepatitis C.
Cirrhosis of the liver can cause many different symptoms. Some of these symptoms are high blood pressure in the veins that travel to the liver; a buildup of fluid in the abdomen, called ascites; easy bruising or bleeding; veins becoming larger than normal, especially in the stomach and esophagus; jaundice (a yellowing of the skin); and brain damage.
Hepatitis C can also cause some rare problems (problems which do not happen very often), which affect parts of the body outside of the liver. One rare problem that Hepatitis C can cause is Sjögren's syndrome, an autoimmune disorder (or a disorder where the body's system of defenses attacks itself). Hepatitis C can also cause a lower-than-normal number of blood platelets (the part of the blood which causes blood to clot; without enough platelets, a person can have bleeding problems, or can start bleeding and be unable to stop. Other rare problems that Hepatitis C can cause are chronic (long-lasting) skin disease; non-Hodgkin's lymphoma (a type of cancer); and diabetes (where a person's body does not make or use enough insulin, an important hormone that controls the level of sugar in the blood).
Hepatitis C is caused by the Hepatitis C virus (HCV). In the scientific system that names and organizes viruses, the Hepatitis C virus is part of the "hepacivirus" genus in the family "Flaviviridae". There are seven major types of HCV, called "genotypes". In the United States, the first genotype of HCV causes 70% of all cases of Hepatitis C (or 7 out of every 10); the second genotype causes 20% (or 2 out of every 10); and each of the other genotypes causes 1% (or 1 out of every 100 cases). Thr first genotype is also the most common in South America and Europe.