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# File 'lib/dsa_visualizer/data_structures/stack.rb', line 45
def self.demo
Visualizer.("STACK - Core Level Visualization")
Visualizer.print_section("1. Stack Concept (LIFO)")
puts "\nLast In, First Out - like a stack of plates"
puts "Operations: push (add), pop (remove), peek (view top)"
Visualizer.print_section("2. Implementation Comparison")
ruby_code = " class Stack\n def initialize\n @items = [] # Dynamic array\n end\n \n def push(item)\n @items.push(item) # O(1) amortized\n end\n \n def pop\n @items.pop # O(1)\n end\n end\n RUBY\n\n cpp_code = <<~CPP\n class Stack {\n std::vector<int> items;\n public:\n void push(int item) {\n items.push_back(item); // O(1) amortized\n }\n \n int pop() {\n int top = items.back();\n items.pop_back(); // O(1)\n return top;\n }\n };\n CPP\n\n explanation = \"Both use dynamic arrays internally. Ruby's Array and C++'s std::vector provide O(1) push/pop at end. Alternative: linked list implementation trades memory for guaranteed O(1) operations.\"\n \n Visualizer.print_comparison(ruby_code, cpp_code, explanation)\n \n # Demo Operations\n Visualizer.print_section(\"3. Stack Operations\")\n tracker = MemoryTracker.new\n stack = Stack.new\n \n # Push operations\n Visualizer.print_step(1, \"Pushing elements: 10, 20, 30\")\n [10, 20, 30].each do |val|\n stack.push(val)\n tracker.track_operation(\"Push\", \"Pushed \#{val}\")\n puts stack.visualize\n end\n \n puts \"\\n\u{1F50D} Push Internals (Ruby):\"\n puts \" 1. Check array capacity\"\n puts \" 2. If full: allocate new array (2\u00D7 size)\"\n puts \" 3. Copy existing elements (if resized)\"\n puts \" 4. Add element at end\"\n puts \" 5. Increment size counter\"\n puts \" Amortized O(1) - occasional O(n) resize\"\n \n puts \"\\n\u{1F50D} Push Internals (C++):\"\n puts \" 1. Check vector capacity\"\n puts \" 2. If full: allocate new memory\"\n puts \" 3. Move/copy elements (if resized)\"\n puts \" 4. Place element at end\"\n puts \" 5. Update size\"\n puts \" Amortized O(1) - same as Ruby\"\n \n # Peek operation\n Visualizer.print_step(2, \"Peeking at top element\")\n top = stack.peek\n puts \"Top element: \#{top}\".colorize(:yellow)\n puts stack.visualize\n tracker.track_operation(\"Peek\", \"Viewed top: \#{top}\")\n \n # Pop operations\n Visualizer.print_step(3, \"Popping elements\")\n 2.times do\n popped = stack.pop\n tracker.track_operation(\"Pop\", \"Popped \#{popped}\")\n puts \"\\nPopped: \#{popped}\".colorize(:red)\n puts stack.visualize\n end\n \n puts \"\\n\u{1F50D} Pop Internals:\"\n puts \" Ruby:\"\n puts \" 1. Check if empty (raise error if true)\"\n puts \" 2. Get last element\"\n puts \" 3. Decrement size\"\n puts \" 4. Return element\"\n puts \" O(1) operation\"\n \n puts \"\\n C++:\"\n puts \" 1. Access last element (no bounds check)\"\n puts \" 2. Call destructor if needed\"\n puts \" 3. Decrement size\"\n puts \" 4. Return value\"\n puts \" O(1) operation\"\n \n # Memory Layout\n Visualizer.print_section(\"4. Memory Layout\")\n \n puts \"\\n\u{1F4E6} Array-based Stack Memory:\"\n puts \" Ruby:\"\n puts \" Stack object \u2192 Array object \u2192 [ref1, ref2, ref3, ...]\"\n puts \" Each element is object reference\"\n puts \" Overhead: Array header + references\"\n \n puts \"\\n C++:\"\n puts \" Stack object \u2192 vector \u2192 [val1, val2, val3, ...]\"\n puts \" Direct values in contiguous memory\"\n puts \" Overhead: vector metadata only\"\n \n # Use Cases\n Visualizer.print_section(\"5. Real-World Use Cases\")\n \n puts \"\\n\u{1F4DA} Common Applications:\"\n puts \" 1. Function call stack (recursion)\"\n puts \" 2. Undo/Redo operations\"\n puts \" 3. Expression evaluation (postfix)\"\n puts \" 4. Backtracking algorithms\"\n puts \" 5. Browser history (back button)\"\n \n puts \"\\n\u{1F4A1} Example: Function Call Stack\"\n puts \" def factorial(n)\"\n puts \" return 1 if n <= 1\"\n puts \" n * factorial(n - 1) # Each call pushed to stack\"\n puts \" end\"\n puts \"\\n Call stack for factorial(3):\"\n puts \" \u2502 factorial(1) \u2502 \u2190 TOP (returns 1)\"\n puts \" \u251C\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2524\"\n puts \" \u2502 factorial(2) \u2502 (waits for result)\"\n puts \" \u251C\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2524\"\n puts \" \u2502 factorial(3) \u2502 (waits for result)\"\n puts \" \u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2518\"\n \n tracker.print_summary\n \n Comparator.compare_complexity(\n \"Stack Operations\",\n \"Push/Pop: O(1) amortized, Peek: O(1)\",\n \"Push/Pop: O(1) amortized, Peek: O(1)\",\n \"Both implementations have same complexity. C++ is faster due to direct value storage vs Ruby's object references.\"\n )\n \n puts \"\\n\\n\u{1F3AF} Key Takeaways:\".colorize(:green).bold\n puts \" 1. Stack is LIFO - Last In, First Out\"\n puts \" 2. Array-based implementation provides O(1) operations\"\n puts \" 3. Both Ruby and C++ use dynamic arrays internally\"\n puts \" 4. Perfect for reversing, backtracking, and nested structures\"\n puts \" 5. Function calls use stack internally (call stack)\"\nend\n"
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