vault backup: 2024-12-01 23:50:59

Data Structures/GPT Answers to Past Paper/Question 7.md

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+# Compare and contrast a queue with a stack.
+
+### **Comparison of Queue and Stack**
+
+|**Aspect**|**Stack**|**Queue**|
+|---|---|---|
+|**Definition**|A stack is a collection of elements that follows the **Last-In, First-Out (LIFO)** principle: the last element added is the first one removed.|A queue is a collection of elements that follows the **First-In, First-Out (FIFO)** principle: the first element added is the first one removed.|
+|**Primary Operations**|- **Push**: Add an element to the top of the stack.  <br>- **Pop**: Remove the top element of the stack.  <br>- **Peek/Top**: View the top element without removing it.|- **Enqueue**: Add an element to the back of the queue.  <br>- **Dequeue**: Remove the element from the front of the queue.  <br>- **Front**: View the element at the front without removing it.|
+|**Order of Removal**|LIFO: Last element inserted is the first to be removed.|FIFO: First element inserted is the first to be removed.|
+|**Structure**|Operates on a single end of the collection (top).|Operates on both ends: elements are added at the back and removed from the front.|
+|**Real-World Analogy**|A stack of plates: the last plate added is the first one removed.|A line (queue) at a ticket counter: the first person in line is the first one served.|
+|**Applications**|- Function call stack  <br>- Undo operations in software  <br>- Backtracking algorithms (e.g., maze solving)  <br>- Expression evaluation and parsing|- Task scheduling (e.g., printer queue)  <br>- Breadth-first search (BFS) in graphs  <br>- Data buffers (e.g., IO buffers)  <br>- Handling requests in web servers|
+|**Performance**|Both `push` and `pop` are O(1)O(1)O(1) operations in most implementations.|Both `enqueue` and `dequeue` are O(1)O(1)O(1) operations in most implementations.|
+|**Types/Variants**|- Simple Stack  <br>- Double Stack  <br>- Min/Max Stack (keeps track of min/max values)|- Simple Queue  <br>- Circular Queue  <br>- Priority Queue (elements removed based on priority, not order)  <br>- Deque (Double-Ended Queue)|
+
+---
+
+### **Key Differences**
+
+|**Aspect**|**Stack**|**Queue**|
+|---|---|---|
+|**Access Pattern**|LIFO (Last-In, First-Out)|FIFO (First-In, First-Out)|
+|**Addition (Insert)**|Always at the top of the stack.|Always at the back of the queue.|
+|**Removal (Delete)**|Always from the top of the stack.|Always from the front of the queue.|
+|**Flexibility in Ends**|Operates only on one end (top).|Operates on both ends (front and back).|
+
+---
+
+### **Real-World Examples**
+
+#### **Stack Examples**:
+
+1. **Undo Feature in Text Editors**:
+    - When you perform actions, they are stored in a stack. Undoing removes the last action first.
+2. **Browser Back Button**:
+    - Tracks visited pages in a stack; the last page visited is the first to be returned when you press "Back."
+
+#### **Queue Examples**:
+
+1. **Ticket Counter**:
+    - People stand in line (queue), and the first person in line is served first.
+2. **Task Scheduling**:
+    - Jobs sent to a printer are handled in the order they are received (FIFO).
+
+---
+
+### **Summary**:
+
+- A **stack** is suitable for tasks where the most recent action needs to be undone or processed first (**LIFO**).
+- A **queue** is ideal for tasks where the first action needs to be processed first (**FIFO**).