快排---非递归&递归实现

递归的核心是栈；可构造辅助栈实现非递归。

#include<iostream>
#include <stdio.h> 
#include <stack> 
#include <algorithm>
using namespace std;

int partion(int* arr, int low, int high)
{
    if (low == high) {
        return low;
    }
    int part = arr[low];
    while (low < high)
    {
         while (high > low && arr[high] >= part)
        {
            high --;
        }
        swap(arr[low], arr[high]);

        while (low < high && arr[low] <= part)
        {
            low ++;
        }
        swap(arr[low], arr[high]);
        
    }  
    arr[low] = part;
    return low;
}

//递归写法
void quickSort1(int* arr, int low, int high)
{
    if (low ==high) {
        return;
    }
    int part_index = partion(arr, low, high);
    if (part_index > low) {
        quickSort1(arr, low, part_index -1);
    }
    if (part_index < high) {
        quickSort1(arr, part_index + 1, high);
    }
}

//非递归写法
void quickSort2(int* arr, int low, int high)
{
    stack<int> sk;
    if (low < high) {
        int part_index = partion(arr, low, high);
        if (low < part_index - 1) {
            sk.push(low);
            sk.push(part_index - 1);
        }
        if (part_index + 1 < high) {
            sk.push(part_index + 1);
            sk.push(high);
        }
        while (!sk.empty())
        {
            int high_sk = sk.top();
            sk.pop();
            int low_sk = sk.top();
            sk.pop();
            
            part_index = partion(arr, low_sk, high_sk);
            
            if (low_sk < part_index - 1) {
                sk.push(low_sk);
                sk.push(part_index - 1);
            }
            if (part_index + 1 < high) {
                sk.push(part_index + 1);
                sk.push(high_sk);
            }
        }
    }
}


int main()
{
    int a[8] = {4, 2, 6, 7, 9, 5, 1, 3};
　　//　
    quickSort2(a, 0, 7);
    
    for(int i = 0; i < 8; i++) {
        cout << a[i] << endl;
    }
    return 0;
}