C++ 一些基本算法练习

以体会思想为目的，进行c++算法基本练习。

涉及二分法，迭代器移动，快排。

#include <iostream>
#include <string>
using namespace std;
/*
二分法找元素，核心思想是二分判断
*/
int find_element_in_array(int *a,int length,int element)
{
	int begin, end, mid;
	begin = 0;
	end = length-1;
	mid = (end + begin) / 2;
	while (begin < end && a[mid] != element)
	{	
		if (a[mid] > element)
		{
			//cout <<a[mid]<< endl;
			end = mid-1;
		}
		if (a[mid] < element)
		{
			//cout << a[mid] << endl;
			begin = mid+1;	
		}
		mid = (end + begin) / 2;
	}
	if (element == a[mid])
	{
		cout << "element : " << element << " a[mid] : " << a[mid] << endl;
	}
	else
	{
		cout << "not found " << element<<endl;
	}
	return 0;
}
void main_find_element_in_array()
{
	int array1[10] = { 1, 5, 23, 33, 45, 57, 59, 76, 87, 93 };
	find_element_in_array(array1, 10, 59);
}
/*
第一种，以空间换时间，开辟一个新空间，利用尾迭代器递减，遍历一次size（）
*/
void string_reverse_one(const string str)
{
	string temp="";
	auto end = str.cend();
	for (auto s : str)
	{
		temp += *(--end);
	}
	cout << temp << endl;
}
void main_string_reverse_one()
{
	string s = "my name is kobe";
	string_reverse_one(s);
}
/*
第二种，字符串翻转的核显思想是，利用迭代器，通过交换头尾迭代器的值，这样只需遍历size（）/2
*/
void string_reverse_two(string &str)
{
	auto begin = str.begin();
	auto end = str.end() - 1;
	if (str.size() % 2 != 0)
	{
		while (begin != end)
		{
			auto t = *end;
			*end = *begin;
			*begin = t;
			begin++;
			end--;
		}
	}
	if (str.size() % 2 == 0)
	{	
		int cout = 0;
		while (cout != (str.size()/2))
		{
			auto t = *end;
			*end = *begin;
			*begin = t;
			begin++;
			end--;
			cout++;
		}
	}
}
void main_string_reverse_two()
{
	string s = "my name is kobe!";
	string_reverse_two(s);
	cout << s << endl;
}


/*
快排的核心思想是，找到当前列表的第一个元素应该在的位置！
然后递归剩下位置的数据
*/
void swap(int *a, int low, int high)
{
	int temp;
	temp = a[low];
	a[low] = a[high];
	a[high] = temp;
}
int Partition(int *a, int low, int high)
{
	int pivotkey = a[low];
	while (low < high)
	{
		while (low < high && a[high] >= pivotkey)
			high--;
		swap(a, low, high);
		while (low < high && a[low] <= pivotkey)
			low++;
		swap(a, low, high);
	}
	return low;
}
void Qsort(int *a, int low, int high)
{
	int pivot;
	if (low < high)
	{
		pivot = Partition(a, low, high);
		Qsort(a, low, pivot-1);
		Qsort(a, pivot+1, high);
	}
}
void quick_sort(int *a, int length)
{
	length = length - 1;
	Qsort(a, 0, length);
}
void main_quick_sort()
{
	int array1[10] = { 12, 5, 53, 83, 45, 7, 69, 56, 87, 93 };
	quick_sort(array1,10);
	for (int i : array1)
	{
		if (i!=0)
			cout << i << ' ';
	}
}


void main()
{	
	cout << "二分法查找" << endl;
	main_find_element_in_array();
	cout << "翻转字符串方法1" << endl;
	main_string_reverse_one();
	cout << "翻转字符串方法2" << endl;
	main_string_reverse_two();
	cout << "快排排序" << endl;
	main_quick_sort();
}