Stacks and Queues Dr. Andrew Wallace PhD BEng(hons) EurIng

Overview In and out Stack operations Stack implementation Queue operations Queue implementation Complexity

In and Out Data Memory Address Data Memory Address Data Memory Address Data Memory Address Data Memory Address Data Memory Address Data Memory Address Data Memory Address Stack Queue

In and out LIFO Last in first out FIFO First in first out

Stack Operations S[1 … S.top] Is empty Push Pop

Stack Operations IsEmpty(S) if S.top == null return TRUE else return FALSE

Stack Operations Push(s.x) S.top = S.top + 1 S[S.top] = s.x data S.top s.x

Stack Operations Pop(S) ASSERT(!IsEmpty(S)) S.top = S.top -1 return S[S.top + 1] data S.top s.x

Stack Implementation Array Linked list

Stack Implementation s.tops.top s.tops.top

Queue Operations Q[Q.head … Q.tail] Enqueue(Q.tail) Dequeue(Q.head)

Queue Operations Enqueue(Q.x) Q.tail = Q.x if Q.tail == Q.length Q.tail = 1 else Q.tail = Q.tail + 1 data Q.head Q.tail Q.x Q.tail

Queue Operations Dequeue(Q) Q.x = Q[Q.head] if Q.head == Q.length Q.head = 1 else Q.head = Q.head + 1 return Q.x data Q.tail data Q.head Q.x

Queue Implementation Array Linked list

Queue Implementation Q.headQ.head Q.TailQ.Tail Q.TailQ.Tail

Queue Implementation Q.headQ.head 90 Q.TailQ.Tail Q.TailQ.Tail

Complexity Pop(S) ASSERT(!IsEmpty(S)) S.top = S.top -1 return S[S.top + 1] Dequeue(Q) Q.x = Q[Q.head] if Q.head == Q.length Q.head = 1 else Q.head = Q.head + 1 return Q.x Q(1)

Questions?