prg15_2.cpp

数据结构c++语言描述stl版 威廉兄弟的好书,值得看,这是配书代码

// File: prg15_2.cpp
// the program compares the performance of heapsort, mergesort,
// quicksort, and the insertion sort. vectors v1,v2,v3, and v4
// are initialized with the same 100,000 random numbers in the
// range 0 to 999999. the program calls the function timeSort()
// with each vector as an argument and arguments that identify
// the sorting algorithm. the function times the sorting of the
// vector and calls outputFirst_Last() to display the first and
// last 5 values in the sorted vector. the function timeSort()
// then outputs the name of the sorting algorithm and the time
// it required to sort the vector. the program illustrates the
// general superiority of quicksort and the excellent speed
// of heapsort. mergesort has a slower time because it is not an
// in-place sorting algorithm. the results vividly contrast an
// O(n log n) algorithm with the quadratic insertion sort algorithm

#include <iostream>
#include <string>
#include <vector>
#include <functional>		// greater<T> for heapSort()

#include "d_random.h"		// randomNumber class
#include "d_sort.h"			// vector sorting algorithms
#include "d_timer.h"			// timer class

using namespace std;

// outputs the first 5 and last 5 items in the vector
void outputFirst_Last(const vector<int>& v);

// types of sorts we will test
enum sortType {HEAPSORT, MERGESORT, QUICKSORT,
					INSERTIONSORT};

// apply the specified sort to v and time it.
// output the result using sortName as a descriptive
// label
void timeSort(vector<int>& v ,sortType sort,
				  const string& sortName);
int main()
{
	const int VECTORSIZE = 100000;
   vector<int> v1, v2, v3, v4;    
	int rndNum, i;
	randomNumber rnd;    

   // load the vectors with the same sequence of 100000
	// random numbers in the range 0 to 999999
   for(i=0;i < VECTORSIZE;i++)
	{
		rndNum = rnd.random(1000000);
      v1.push_back(rndNum);
      v2.push_back(rndNum);
      v3.push_back(rndNum);
      v4.push_back(rndNum);
	}
	 
	// time heap sort
   timeSort(v1,HEAPSORT,"Heap sort");
    
   // repeat process for the merge sort
   timeSort(v2,MERGESORT,"Merge sort");
  
   // repeat process for the quick sort
   timeSort(v3,QUICKSORT,"Quick sort");
  
   // repeat process for the insertion sort
   timeSort(v4,INSERTIONSORT,"Insertion sort");
   
	return 0;
}

void outputFirst_Last(const vector<int>& v)
{
	// capture vector size in n
	int i, n = v.size(), m = 5;
    
	// if the vector size is 10 or less, just
	// output the whole vector
	if (n <= 10)
		m = n;

	// output m elements
	for(i=0;i < m;i++)
		cout << v[i] << "  ";

	// for n > 10, output "..." and the last 5 elements
	if (n > 10)
	{
		cout << ". . .  ";
		for(i= n-5; i < n; i++)
			cout << v[i] << "  ";
	}
	cout << endl;
}

void timeSort(vector<int>& v, sortType sort,
				  const string& sortName)
{
	timer t;

   // start timing and then sort vector arr
   t.start();

   switch(sort)
	{
		case HEAPSORT:			heapSort(v, greater<int>());
									break;
      case MERGESORT:		mergeSort(v, 0, v.size());
									break;
      case QUICKSORT:		quicksort(v, 0, v.size());
									break;
      case INSERTIONSORT:	insertionSort(v);
									break;
	}
	t.stop();
    
	// output the first 5 and last 5 elements of sorted vector
	outputFirst_Last(v);

	cout << sortName << " time is " << t.time() << endl << endl;
}

/*
Run:

8  11  45  55  61  . . .  999956  999961  999969  999972  999985
Heap sort time is 0.07

8  11  45  55  61  . . .  999956  999961  999969  999972  999985
Merge sort time is 0.39

8  11  45  55  61  . . .  999956  999961  999969  999972  999985
Quick sort time is 0.04

8  11  45  55  61  . . .  999956  999961  999969  999972  999985
Insertion sort time is 33.909
*/