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Stacks a data structure which stores data in a Last-in First-out manner (LIFO) has a pointer called TOP can be implemented by either Array or Linked List

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Stack 3000 4000 2000 1000 top 0 1 2 3 4 5 max index = 5 start index = 0 Two operations: PUSH – puts an item on the top of the stack POP – takes an item from the top of the stack 3 is the top of the stack

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Stack - pop 3000 4000 2000 1000 top 0 1 2 3 4 5 What value do we get if we pop from the stack? Answer: 1000

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3000 4000 2000 top 0 1 2 3 4 5 Stack - pop and the top of the stack changes to ? top Let’s pop once more..

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3000 4000 0 1 2 3 4 5 top 2000 is popped… top and top changes to 1 Stack - pop

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to what extent do we pop? 3000 4000 0 1 2 3 4 5 top Let’s keep popping…

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4000 0 1 2 3 4 5 top and now top is 0 let’s pop more..

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0 1 2 3 4 5 top and now top is -1 can we still pop? before popping we need to check the top

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3000 4000 0 1 2 3 4 5 top pushing an item to stack causes top to move upward first then store the item Stack - push top 5000 To what extent do we push?

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Pseudocode for push 1. increment top 2. put item on stack 3000 4000 0 1 2 3 4 5 top 5000 5000 5000 5000 What if top is the last index? Can we still push? NO !!! when top is max index, we need to signal stack is full

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Pseudocode for push 1. increment top 2. put item on stack 3. if top = max index then isFULL=TRUE 3000 4000 0 1 2 3 4 5 top 5000 5000 5000 5000 Are we done? No, we need to check first if the stack is full Before we proceed to push an item

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Pseudocode for push 1. If not isFULL then 2. increment top 3. put item on stack 4. if top = max index then 5. isFULL=TRUE 6. else 7. isFULL = FALSE 8. else 9. display “stack full,push not allowed”

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Pseudocode for Pop 1. If not isEmpty then 2. getitem=Stack[top] 3. top=top -1 4. if top < first index then 5. isEmpty = True 6. else 7. isEmpty=False 8. Else 9. display “stack empty, nothing to pop”

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Applications of Stack Checking of balanced parenthesis Tracking memory addresses before and after invoking a function Arithmetic operations evaluation Program compilation

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Queue Data structure which stores data in First In – First Out (FIFO)

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1020405 Queue front rear Two operations: Enqueue – item after the rear Dequeue – get item on the front Did you observe queues in your day to day life?

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Queue 1020405 front rear Enqueue 1.If queue is not full 2. add 1 to rear 3. put item on rear if rear is max index if rear is max index isFull = TRUE isFull = TRUE else else isFull=FALSE isFull=FALSE

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1020405 front rear Dequeue 1.If queue is not empty 2.get item from front 3.Add 1 to front if front = rear if front = rear isEmpty = TRUE isEmpty = TRUE else else isEmpty=FALSE isEmpty=FALSE Queue

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Applications of Queue Printing queue Manage job requests

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1 Data Structures - Part II CS215 Lecture #8. Stacks Last-In-First-Out (LIFO) Stacks are often used in programming when data will need to be used.

1 Data Structures - Part II CS215 Lecture #8. Stacks Last-In-First-Out (LIFO) Stacks are often used in programming when data will need to be used.

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