算法和数据结构项目练习2-最小堆和最大堆

项目介绍

1. 从txt文件中读取输入(在本例中为整数)。

2. 将其添加到当前堆的最后一个元素。

3.把它筛到正确的位置，做一个最小堆。

4. 读取完所有整数后，打印出最小堆数组的前五个元素。

5. 之后将数组转换为最大堆并再次打印前5个元素。

不使用类或STL来实现堆。堆使用固定大小的整数数组来实现。

文件输入为任意的整数，本例的数量为100个整数。

代码实现

先声明函数，中间是main，函数的定义我们放在最后。

本项目的核心是对堆结构的了解，如最小堆和最大堆的新元素的插入与排序。

可以看一下我的这篇文章来简单理解：
https://blog.youkuaiyun.com/Jifu_M/article/details/112792801

#include<iostream>
#include<string>
#include<fstream>

using namespace std;


const int MAX = 200;
void MaxHeapAdjust(int array[], int i, int nLength);
void MaxHeapSort(int array[], int length);
int MinHeapAdjust(int array[], int i, int nLength);
void MinHeapSort(int array[], int length);

int main()
{

	int  Array[MAX];
	int index = 0;
	string a;//	display a prompt for the file name
	cout << "Please enter the filename: " << endl;
	cin >> a;

	ifstream read;//read in the file name
	read.open(a.c_str());//	try to open the file
	if (!read)//if the file fails to open print an error message on the screenand exit
	{
		cout << "Error! Can't find the file" << endl;
		exit(1);
	}


	while (!read.eof())
	{
		read >> Array[index];
		if (read.eof())
			break;

		index++;
		MinHeapSort(Array, index);//insert the int into the array(to make a min heap)
	}
	read.close();//	close the file



	cout << "The first 5 elements in min heap are:" << endl;//print the first 5 elements of the heap
	for (int i = 0; i < 5; ++i)
	{
		cout << Array[i] << endl;
	}


	cout << "The first 5 elements in max heap are:" << endl;

	//Max Heap Sort
	MaxHeapSort(Array, index);//to make a max heap
	for (int i = 0; i < 5; ++i)//print the first 5 elements of the heap
	{
		cout << Array[i] << endl;
	}
	return 0;	

}

int MinHeapAdjust(int array[], int i, int nLength)
{
	int nChild;
	int tool;
	int swap = 0;
	for (; 2 * i + 1 < nLength; i = nChild)
	{
		//child's position = 2*father's position+1
		nChild = 2 * i + 1;
		//get the min child 
		if (nChild < nLength - 1 && array[nChild + 1] < array[nChild])
			++nChild;

		if (array[i] > array[nChild])
		{
			tool = array[i];
			array[i] = array[nChild];
			array[nChild] = tool;
			swap = 1;//swap happen

		}
		else
			//break,swap not happen
			break;
	}
	return swap;
}
//adjust to min heap
void MinHeapSort(int array[], int length)
{
	int f;
	// length/2-1 is length's father position 
	for (int i = length / 2 - 1; i >= 0; i = i / 2 - 1) {
		f = MinHeapAdjust(array, i, length);
		if (f == 0) {
			break;
		}
	}
}
void MaxHeapAdjust(int array[], int i, int nLength)
{
	int nChild;
	int nTool;
	for (; 2 * i + 1 < nLength; i = nChild)
	{
		//child's position = 2*father's position+1
		nChild = 2 * i + 1;
		//get the max child 
		if (nChild<nLength - 1 && array[nChild + 1]>array[nChild])
			++nChild;

		if (array[i] < array[nChild])
		{
			nTool = array[i];
			array[i] = array[nChild];
			array[nChild] = nTool;
		}
		else
			//break
			break;
	}
}
//Max Heap Sort
void MaxHeapSort(int array[], int length)
{

	//length/2-1 is the last position that not leaf
	for (int i = length / 2 - 1; i >= 0; --i)
		MaxHeapAdjust(array, i, length);

}

程序输出如下：