adding lab

labs/priority_queues/README.md

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+# Lab 10 — Priority Queues
+
+In this lab, you will use binary heaps to implement the priority queue container. Start by downloading the files:
+
+[priority_queue.h](priority_queue.h) [test_pq.cpp](test_pq.cpp)
+
+The code provided in these files is straightforward. test_pq.cpp is a driver and test program, while priority_queue.h is a skeleton implementation. Please take a careful look. You will complete the implementation and add to the main program in lab. In your implementation, be careful when subtracting 1 from an unsigned int whose value is 0; it is not -1!
+
+## Checkpoint 1:
+
+Implement and test the push (a.k.a. insert) and the check_heap functions. Recall that push depends on the percolate_up functionality. check_heap, which works either with the heap member variable or with a vector provided from the outside, determines if the vector is properly a heap, meaning that each value is less than or equal to the values of both of its children (if they exist).
+
+**To complete this checkpoint**: Show a TA or mentor your debugged implementation and discuss the running time of both insert and check_heap.
+
+## Checkpoint 2:
+
+Implement and test the pop (a.k.a. delete_min) function and the constructor that builds a valid heap from a vector of values that is in no particular order. Both of these depend on proper implementation of the percolate_down function.
+
+**To complete this checkpoint**: Show a TA or mentor these additions and the test output.
+
+## Checkpoint 3:
+
+Finally, write and test the non-member function that sorts a vector by doing a heap sort. This code should sort the data “in place” and not require a large scratch space (e.g., another vector or list or another priority queue) to store a copy of the data as it is being sorted.
+
+**To complete this checkpoint**: Show a TA or mentor your completed and debugged heap sort code.

labs/priority_queues/priority_queue.h

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+#ifndef priority_queue_h_
+#define priority_queue_h_
+
+#include <iostream>
+#include <vector>
+#include <cassert>
+
+
+template <class T>
+class priority_queue {
+private:
+  std::vector<T> m_heap;
+
+public:
+  priority_queue() {}
+
+  priority_queue( std::vector<T> const& values )
+  {
+  }
+
+  const T& top() const 
+  {
+    assert( !m_heap.empty() );
+    return m_heap[0]; 
+  }
+
+  void push( const T& entry )
+  {
+  }
+
+  void pop() 
+  {
+    assert( !m_heap.empty() );
+  }
+
+  int size() { return m_heap.size(); }
+  bool empty() { return m_heap.empty(); }
+
+
+  //  The following three functions are used for debugging.
+
+  //  Check to see that internally the heap property is realized.
+  bool check_heap( )
+  {
+    return this->check_heap( this->m_heap );
+  }
+
+  //  Check an external vector to see that the heap property is realized.
+  bool check_heap( const std::vector<T>& heap )
+  {
+  }
+
+  //  A utility to print the contents of the heap.  Use it for debugging.
+  void print_heap( std::ostream & ostr )
+  {
+    for ( unsigned int i=0; i<m_heap.size(); ++i )
+      ostr << i << ": " << m_heap[i] << std::endl;
+  }
+  
+};
+
+
+template <class T>
+void heap_sort( std::vector<T> & v )
+{
+}
+
+#endif

labs/priority_queues/test_pq.cpp

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+#include <iostream>
+#include <vector>
+
+#include "priority_queue.h"
+
+
+int main() {
+
+  priority_queue<int> pq_int;
+
+  std::cout << "****************\n"
+            << "* Checkpoint 1 *\n"
+            << "****************" << std::endl;
+  
+  std::vector<int> heap_vector, empty_vector, one_vector;
+  one_vector.push_back( 4 );
+  heap_vector.push_back( 2); heap_vector.push_back(11); heap_vector.push_back( 7);
+  heap_vector.push_back(13); heap_vector.push_back(29); heap_vector.push_back( 8);
+  heap_vector.push_back( 9); heap_vector.push_back(27); heap_vector.push_back(21);
+  heap_vector.push_back(37); heap_vector.push_back(40); heap_vector.push_back(16);
+  std::vector<int> non_heap_vector( heap_vector );
+  non_heap_vector[5] = 23;  //  less than its parent
+
+  std::cout << "Testing if check_heap works." << std::endl
+            << "An empty vector is a heap.  check_heap = " << pq_int.check_heap(empty_vector) << std::endl
+            << "A one-element vector is also a heap.  check_heap = "  
+            << pq_int.check_heap(one_vector) << std::endl
+            << "A manually constructed heap.  check_heap = " << pq_int.check_heap(heap_vector) << std::endl
+            << "A change at one location creates a non-heap.  check_heap = " 
+            << pq_int.check_heap(non_heap_vector) << std::endl;
+  
+  pq_int.push( 5 );
+  pq_int.push( 13 );
+  pq_int.push( 3 );
+  pq_int.push( 11 );
+  pq_int.push( 6 );
+  pq_int.push( 23 );
+  pq_int.push( 8 );
+  pq_int.push( 12 );
+  
+  std::cout << "After 8 push operations the size is " << pq_int.size() << std::endl
+            << "The top, which should be 3, is " << pq_int.top() << std::endl
+            << "The call to pq.int.empty() returns " << pq_int.empty() << std::endl
+            << "pq_int.check_heap() = " << pq_int.check_heap() << std::endl;
+
+  std::cout << "\nHere is the actual heap.  Values should be 3, 6, 5, 12, 11, 23, 8, 13\n";
+  pq_int.print_heap( std::cout );
+  
+  /*
+  std::cout << "\n\n"
+            << "****************\n"
+            << "* Checkpoint 2 *\n"
+            << "****************" << std::endl;
+  
+  pq_int.pop();
+  std::cout << "After one pop, the size should be 7.  It is " << pq_int.size() << std::endl
+            << "and the top value should be 5.  It is " << pq_int.top() << std::endl;
+  pq_int.pop(); pq_int.pop();
+  std::cout << "After two more pops, the size should be 5.  It is " << pq_int.size() << std::endl
+            << "and the top value should be 8.  It is " << pq_int.top() << std::endl;
+  pq_int.push( 1 );
+  std::cout << "Another push should make the top value 1.  It is " << pq_int.top() << std::endl;
+  pq_int.pop(); pq_int.pop();    pq_int.pop(); pq_int.pop();    pq_int.pop(); pq_int.pop(); 
+  std::cout << "After six more pops, the pq should be empty.  pq_int.empty() = " << pq_int.empty() << std::endl;
+  
+  std::vector<float> v;
+  priority_queue<float> pq_f(v);
+  std::cout << '\n' << "Now we are trying construction from a vector.\n"
+            << "When the vector is empty, here is the value of pq_f.empty() = " << pq_f.empty() << std::endl;
+
+  v.push_back(13.5); v.push_back(11.1); v.push_back(11.1); v.push_back(-4);
+  v.push_back(14.3); v.push_back(4.5);  v.push_back(8.5); v.push_back(27.6);
+  v.push_back(2.3);  v.push_back(15.2); v.push_back(23.1); v.push_back(12.5);
+  priority_queue<float> pq_float(v);
+  std::cout << "After constructing from a 12-value vector, the size is " << pq_float.size() << std::endl
+            << "the top, which should be -4 is " << pq_float.top() << std::endl
+            << "and check_heap returns " << pq_float.check_heap() << std::endl;
+  */
+
+  /*
+  std::cout << "\n\n"
+            << "****************\n"
+            << "* Checkpoint 3 *\n"
+            << "****************" << std::endl;
+  
+  heap_sort( v );
+  int order_errors = 0;
+  for ( unsigned int i=0; i<v.size()-1; ++i )
+    if ( v[i] > v[i+1] ) order_errors ++ ;
+
+  std::cout << "After running heap sort, the size of the vector, which still should be 12 is " << v.size()
+            << "\nand there are " << order_errors << " ordering errors\n"
+            << "The resulting vector is\n";
+  for ( unsigned int i=0; i<v.size(); ++i )
+    std::cout << i << ": " << v[i] << '\n';
+
+  std::cout << "\nRunning heap sort on an empty vector... " << std::endl;
+  v.clear();
+  heap_sort(v);
+  std::cout << "produces a vector that is " << (v.empty() ? "empty" : "NOT empty") << std::endl;
+  */
+  
+  return 0;
+}