# CS 314 Final Exam Vocabulary Terms

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Novak's CS 314 final vocabulary list.

### A*

a heuristic search algorithm that attempts to find a desired goal using a heuristic function to estimate the distance from a given node to the goal.

### abstract data type

a description of operations on a data type that could have multiple possible implementations.

### acyclic

describes a graph with no cycles (circular paths).

a representation of a graph in which each node has a list of nodes that are adjacent to it, i.e. connected to it by an arc.

a representation of a graph in which a boolean matrix contains a 1 at position (i,j) iff there is an arc from node i to node j.

### ancestors

in a tree, the union of a node's parent and the parent's ancestors.

### arc

a link between two nodes in a graph.

### array

a contiguous block of memory containing elements of the same type, accessed by numeric index.

### association list

a list of pairs, where each pair has a key and a value associated with the key.

### AVL tree

a self-balancing sorted binary tree, in which the heights of subtrees differ by at most 1.

### B-tree

a tree with a high branching factor, to minimize the number of disk accesses required to access a desired record.

### backtrack

in a tree search, to move back from the node currently being examined to its parent.

### balanced tree

a tree in which the heights of subtrees are approximately equal.

### bandwidth

information transfer rate of a network connection, in bits/second.

### base case

a simple case that can be solved easily, without recursion.

### Big O

an abstracted function that describes the amount of computer time or memory space required by an algorithm, as a function of problem size.

### bijective

describes a relation that is both injective and surjective (one-to-one and onto).

### binary heap

a data structure that implements a complete binary tree within an array, such that every parent node has a value that is less than the value of either of its children.

### binary search

search of a binary tree or other structure, in which the size of the set to be searched is cut in half at each step.

### binary tree

a tree in which each node has at most two children.

### binding

an association of a name with a value.

### binding list

a list structure that represents a set of bindings.

### Boolean matrix

a matrix whose elements are 0 or 1.

### boxed number

a number that is defined as an object, so that it has a runtime type and methods that can be used, e.g. Integer in Java.

### branching factor

in a search tree, the number of children of a given node. Individual nodes will vary, so an average value may be used.

### bucket

a collection, such as a linked list, of values that hash to the same value.

### cache

to save a value locally to save re-computing or transferring it in the future.

### Cartesian product

a set of pairs (x, y) of elements from two sets X and Y.

### child

in a tree, a node pointed to by a parent node.

### circular queue

a queue implemented within an array, where the first element of the array logically follows the last element.

a linked list in which the last element points back to the first element.

### class

in object-oriented programming, a description of a set of similar objects.

### clustering

a situation in which many elements hash to the same hash value.

### collision

when two values to be stored in a hash table have the same hash value.

### comparison

the act of comparing two values to determine which is greater according to some ordering.

### cons

1. in Lisp, the function that constructs a pair of pointers, or basic element of list structure. 2. to make a cons data structure. 3. a cons data structure.

### constructive

describes a function that makes a new data structure but does not modify its arguments.

### critical path

in a PERT chart or scheduling graph, a path from the initial state to the goal such that any increase in time required along the critical path will increase the time to complete the whole project.

### cycle

a circular path in a graph.

### DAG

directed acyclic graph.

### dense graph

a graph such that a large fraction of possible connections among nodes are present, i.e. the number of edges is of the order of the number of vertices squared. cf. sparse graph.

### depth

the number of links between the root of a tree and the leaves.

### depth-first search

a search in which children of a node are considered (recursively) before siblings are considered.

### dereference

to convert from a pointer (address) to the data that is pointed to.

### descendants

all nodes below a given node in a tree.

### design pattern

a pattern that describes a set of similar programs.

### destructive

describes a function that modifies its arguments.

### DFS

depth-first search.

### Dijkstra's algorithm

an optimal greedy algorithm to find the minimum distance and shortest path in a weighted graph from a give start node.

### directed

describes an arc that can only be traversed in one direction, or a graph with such arcs.

### directed acyclic graph

a directed graph with no cycles.

### discrete event simulation

a simulation in terms of events, in which the highest-priority (least time) event is removed from an event queue and executed, which may have the effect of scheduling future events.

### divide and conquer

a problem-solving strategy in which a problem is broken down into sub-problems, until simple subproblems are reached.

### domain

the set of values that are the source values of a mapping.

a linked list in which each element has both forward and backward pointers.

### edge

a link or arc between nodes in a graph.

### exclusive or

a binary Boolean function whose output is 1 if its inputs are different. Abbreviated XOR.

### extendible hashing

another term for hashing with buckets.

### external sort

a sort using external storage in addition to main memory.

### fair

describes a process in which every arriving customer will eventually be served.

### FIFO

first-in, first-out: describes the ordering of a queue.

### filter

a process that removes unwanted elements from a collection.

### first-child/next-sibling

a way of implementing trees that uses two pointers per node but can represent an arbitrary number of children of a node.

### fold

to process a set of items using a specified function; another term for reduce.

### garbage

storage that is no longer pointed to by any variable and therefore can no longer be accessed.

### garbage collection

the process of collecting garbage for recycling.

### gedanken

describes a thought experiment or view of an entity.

### geometric series

a series in which each successive term is multiplied by a constant less than 1, e.g. 1 + 1/2 + 1/4 + 1/8 + ...

### goal

an item (or description of items) being sought in a search.

### grammar

a formal description of a language in terms of vocabulary and rules for writing phrases and sentences.

### graph

a set of nodes and arcs connecting the nodes.

### greedy algorithm

an algorithm that always tries the solution path that appears to be the best.

### hash function

a function that is deterministic but randomizing, i.e. whose output is a relatively small integer that appears to be a random function of the key value.

### heuristic

a function that estimates the distance from a given node to the goal in A* search. More generally, a method that generally gives good advice about which direction to go or how to approach a problem.

A* search.

### immutable

describes a data structure that cannot be changed once it has been created, such as Integer or String in Java.

### in-place

describes a sort that does not require any additional memory.

### injective

describes a mapping in which each element of the domain maps to a single element of the range. Also, one-to-one.

### inorder

an order of processing a tree in which the parent node is processed in between its children.

### insertion sort

an O(n^2) search algorithm that's similar to the way people sort playing cards. Stable, in-place and on-line. First removes element from list, inserts it in the correct position, and repeats until finished.

### interior node

a node of a tree that has children.

### internal sort

a sort using only the main memory of the computer.

### intersection

given two sets, the set of elements that are members of both sets.

### intractable

a problem that is so hard (typically exponential) that it cannot be solved unless the problem is small.

### iterator

an object containing data and methods to iterate through a collection of data, allowing processing of one data item at a time.

### latency

the delay between asking for data from an I/O device and the beginning of data transfer.

### leaf

a tree node containing a contents value but with no children.

### LIFO

last-in, first out: describes the order of a stack.

### linear

name for O(n) algorithm

a pointer to the next element in a linked list.

a sequence of records, where each record contains a link to the next one.

in a hash table, the fraction of the table's capacity that is filled.

### map

in MapReduce, a program that processes an element of the input and emits one or more (key, value) pairs.

### mapping

association of one or more elements of a Range set with each element of a Domain set.

### master

a program that controls a set of other programs or devices.

### max queue

a priority queue in which the maximum element is removed first.

### memory hierarchy

the use of several kinds of memory hardware in a computer system, where the fastest memory (e.g. cache) is smallest, slower memory (e.g. RAM) is larger, and the slowest memory (e.g. disk) is largest.

### memory locality

the processing of data in such a way that data that are located near each other by memory address are accessed nearby in time.

### merge

to combine two ordered linear structures into one.

### merge sort

O(n*log(n)) search algorithm; stable, not in-place; breaks data in half, sorts, merges, repeats.

### min queue

a priority queue in which the minimum element is removed first.

### minimum spanning tree

a tree formed from the nodes of a graph and a subset of its edges, such that all nodes are connected and the total cost of the edges is minimal.

### node

an element of a linked list, tree, or graph, often represented by a data structure.

### null dereference

a runtime error that occurs when an operation such as a method call is attempted on a null pointer.

### object

a data structure that can be identified at runtime as being a member of a class.

### on-line

describes a sorting algorithm that can process items one at a time.

### one-to-one

describes a mapping in which each element of the domain maps to a single element of the range. Also, injective.

### onto

describes a mapping in which each element of the range is the target of some element of the domain. Also, surjective.

### ontology

a description of the kinds of objects that exist in a computer program, e.g. a Java class hierarchy.

### operator

in a search tree, a program that changes a state into a child state, e.g. a move in a game.

### parent

in a tree, a node that points to a given node.

### parsing

analysis of a sentence of a language to determine the elements of the sentence and their relationship and meaning.

### path

a sequence of steps along arcs in a graph.

### pattern

a representation of a class of objects, containing some constant elements in relation to variable elements.

### pattern variable

a part of a pattern that can match variable parts of an input.

### pivot

in Quicksort, a "center" value used in partitioning the set to be sorted.

### pointer

a variable containing the address of other data.

### postorder

an order of processing a tree in which the parent node is processed after its children.

### preorder

an order of processing a tree in which the parent node is processed before its children.

### priority queue

a queue in which the highest-priority elements are removed first; within a priority value, the earliest arrival is removed first.

name for a O(n^2) algorithm

### queue

a data structure representing a sequence of items, which are removed in the same order as they were inserted.

### quick sort

O(n*log(n)) search algorithm; in-place, not stable. Picks a pivot, reorders so lesser objects are in front of pivot, recursively sorting sub-lists of lesser and sub-lists of greater values.

an O(n*k) search algorithm where K = keylength. Stable. Sorts input into bins based on the lowest digit; then combines bins in order and sorts on the next highest digit & so forth.

### random access

describes a data structure or device in which all accesses have the same cost, O(1).

### randomized algorithm

an algorithm in which the data to be processed or the device to process it is randomly selected.

### range

a set of values that are the targets of a mapping.

### recursion

a case where a program calls itself.

### recursive case

a condition of the input data where the data will be handled by call(s) to the same program.

### Red-Black tree

a self-balancing binary tree in which nodes are "colored" red or black. The longest path from the root to a leaf is no more than twice the length of the shortest path.

### reduce

to apply a given function to the elements of a given list. Also, fold.

### reference

a pointer to data.

### reference type

a type in which variables of that type are pointers to objects.

### rehash

to apply a different hashing function to a key when a collision occurs.

### root

the top node of a tree, from which all other nodes can be reached.

### runtime stack

a stack containing a stack frame of variable values for each active invocation of a procedure.

### scalability

the ability of an algorithm or hardware system to grow to handle a larger number of inputs.

### search

to look through a data structure until a goal object is found.

### sentinel

an extra record at the start or end of a data structure such as a linked list, to simplify the processing.

### set difference

given two sets, the set of elements of the first set that are not members of the second set.

to hide similar items with the same name.

### shortest path

the shortest path between a start node and a goal node in a weighted graph. <

### side-effect

any effect of a procedure other than returning a value, e.g. printing or modifying a data structure.

### simple path

a path between two nodes in a graph that does not revisit any intermediate node.

### slack

in a PERT chart or scheduling graph, the amount of time by which the time of an activity could be increased without affecting the overall completion time.

### slave

a program or device that operates under control of a master.

### sort

to modify the order of a set of elements so that a desired ordering holds between them, e.g. alphabetic order.

### sparse array

an array in which most of the elements are zero or missing.

### sparse graph

a graph in which any node is connected to relatively few other nodes. cf. dense graph.

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