Linked lists
A linked list is a collection of nodes, each made up of a reference and a value. Nodes are strung together into a sequence using their references. Linked lists can be used to implement more complex data structures like lists, stacks, queues, and associative arrays.
Single linked list example
This example implements a linked list with many of the same methods as that of the built-in list object.
class Node:
def __init__(self, val):
self.data = val
self.next = None
def getData(self):
return self.data
def getNext(self):
return self.next
def setData(self, val):
self.data = val
def setNext(self, val):
self.next = val
class LinkedList: def __init__(self):
self.head = None
def isEmpty(self):
"""Check if the list is empty""" return self.head is None
def add(self, item):
"""Add the item to the list""" new_node = Node(item) new_node.setNext(self.head) self.head = new_node
def size(self):
"""Return the length/size of the list""" count = 0 current = self.head while current is not None: count += 1 current = current.getNext() return count
def search(self, item):
"""Search for item in list. If found, return True. If not found, return False""" current = self.head found = False while current is not None and not found:
if current.getData() is item:
found = True else: current = current.getNext()
return found
def remove(self, item): """Remove item from list. If item is not found in list, raise ValueError""" current = self.head previous = None found = False while current is not None and not found:
if current.getData() is item: found = True else: previous = current current = current.getNext() if found: if previous is None: self.head = current.getNext()
else:
previous.setNext(current.getNext())
else:
raise ValueError print 'Value not found.'
def insert(self, position, item):
""" Insert item at position specified. If position specified is out of bounds, raise IndexError """ if position > self.size() - 1:
raise IndexError print "Index out of bounds." current = self.head previous = None pos = 0 if position is 0:
self.add(item) else:
new_node = Node(item) while pos < position: pos += 1 previous = current current = current.getNext() previous.setNext(new_node) new_node.setNext(current)
def index(self, item):
""" Return the index where item is found. If item is not found, return None. """ current = self.head pos = 0 found = False while current is not None and not found:
if current.getData() is item: found = True else:
current = current.getNext() pos += 1 if found: pass else:
pos = None
return pos
def pop(self, position = None): """ If no argument is provided, return and remove the item at the head. If position is provided, return and remove the item at that position. If index is out of bounds, raise IndexError """ if position > self.size(): print 'Index out of bounds' raise IndexError current = self.head if position is None: ret = current.getData() self.head = current.getNext() else: pos = 0 previous = None while pos < position: previous = current current = current.getNext() pos += 1 ret = current.getData() previous.setNext(current.getNext()) print ret return ret
def append(self, item): """Append item to the end of the list""" current = self.head previous = None pos = 0 length = self.size() while pos < length: previous = current current = current.getNext() pos += 1 new_node = Node(item) if previous is None: new_node.setNext(current) self.head = new_node else: previous.setNext(new_node)
def printList(self): """Print the list""" current = self.head while current is not None: print current.getData() current = current.getNext()
Usage functions much like that of the built-in list.
ll = LinkedList() ll.add('l') ll.add('H') ll.insert(1,'e') ll.append('l') ll.append('o') ll.printList()
