C++ 一些基本算法练习

#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();
}