Tutorial 5 Stack & Queue, Midtest

1. Tutorial 5Stack & Queue, Midtest

2. Stack • Last In First Out (LIFO) • Stack implemented using Array with top pointer • http://www2.latech.edu/~box/ds/Stack/Stack.html • Stack implemented using Single Link List with head pointer • Probably the best implementation to date? • http://www.cosc.canterbury.ac.nz/people/mukundan/dsal/LinkListAppl.html TOP

3. Queue • First In First Out (FIFO) • Queue implemented as Circular Array • http://maven.smith.edu/~streinu/Teaching/Courses/112/Applets/Queue/myApplet.html • Queue implemented as Single Link List with Tail Pointer • Head pointer (easy for insert/delete) for dequeue • Tail pointer (only easy for insert) for enqueue • This is because of the pointer directions • Probably the best implementation to date? FRONT BACK

4. Student Presentation • T3 Main Backup • CaiJingfangChngJiajie, Colin Tan • Li HuanNurLiyanaBteRoslie • Zhang JianfeiTan Kar Ann • Tanvir Islam Jessica Chin ZetSze • T4 Main Backup • Choy QianNing, JLiewHui Sun • GohKhoonHiang Li Yawen • HanyenknoAfi Tan Peck Luan • Ng Xue Lin SherilynWong Suet Teng, Melissa • T5 Main Backup • JoyeetaBiswasOngKian An • TeoSim Yee Stephanie Tan Yan Hao • Wu Shujun Wang Ruohan • Liu Na Zheng Yang • T6 Main Backup • Zhang Chao Wang Shuling • Chua Yu Tong LauraRasheillaBte Rajah • Koh Yi Ting Brenda Low Wei Chen Gerard J • SiddharthaGanZhi Wei James Rule: Student in “Main” column has priority to answer the assigned question If the student sick/disappear/absent/cannot solve, etc2… the “backup” will take over. If both students are attending the session,I will create variants of the question for the “backup” students.

5. Question 1 (Applications) • Show us 7 applications of Stacks • Show us 7 applications of Queues • Be creative!

6. Question 2 (Stack: Reorder) • Get algorithm to reorder items using one stack! • Requires thinking on Stack operations: push, pop, top/seek • Derive patterns! • Target Sequence 1 = {1, 2, 3, 5, 4} • Target Sequence 2 = {2, 1, 4, 3, 5} • Target Sequence 3 = {5, 2, 4, 3, 1} • Target Sequence 4 = {1, 4, 3, 2, 5} Only Target Sequence 3 is impossible. See StackTest.java for details

7. Question 3 (Stack for Sorting) • Find algorithm to sort items using two stacks! • Requires thinking on Stack operations: push, pop, top/seek • Hint: try sorting these simple numbers using two stacks: • {7, 5}  {5, 7} • {1, 5, 3}  {1, 3, 5} • {4, 3, 2, 1}  {1, 2, 3, 4} • Derive patterns and write your algorithm! • Hint: During the sorting process, one stack will have numbers in ascending order and the other in descending order. • See StackSort.java for details

8. Question 4 (Queue) • What if Queue ADT is implemented using TailedLinkedListbut in different way! • Think about the pros and cons of this strategy! • The ADT Queue “dequeue” operation is performed by “delete head” and ADT Queue “enqueue” operation is performed by “insert from tail” in TailedLinkedList. • Modified operations: • Enqueue: insert from head  straightforward • Dequeue: delete from tail  hard, because adjusting tail pointer is difficult! • No pro, this modified operations are bad! • If you are presented with this kind of question during exam, do not hesitate to answer “there is no pro” rather than leaving your answer blank! • If you insist, you can say that this modified operations can easily tell you “what object is the 2nd last inserted object” …

9. Student Presentation for Tut 6 • Check your email! • If I send you an email, it means that you are assigned to do next week’s questions…

10. Midterm Test Tips • Priority: • Java Revisit: low • ADT: Likely embedded in Linked List/Stack/Queue question • Linked List: we spend two weeks here, most likely this appear as the only short question during midterm test • Stack and Queue: definitely appear • Try: • Mixing and matching various data structure implementations: variant of linked list, implementing stacks or queues using funny data structures, etc…