快速排序的递归和非递归实现 -----C++、JAVA代码实现

快速排序的基本思想是:通过一趟排序将待排记录分割成独立的两部分,其中一部分记录的关键字均比另一部分记录的关键字小,则可分别对这两部分记录继续进行排序，已达到整个序列有序.
快速排序是一种不稳定的排序方法，其平均时间复杂度为:O(NlogN)，最坏的情况是O（N*N）
特别注意：快速排序中用到的Partition函数，它的作用是进行一趟快速排序，返回“参考目标”的最终位置p,经过Partition处理之后,p左边的记录关键字均不大于参考目标,p右边的记录关键字均不小于参考目标。 Partition函数在找出数组中最大或最小的k个记录也很有用.
C++代码如下：

#include <iostream>#include <vector>#include <stack>using namespace std;template <typename Comparable>int partition(vector<Comparable> &vec,int low, int high){    Comparable pivot = vec[low];    while (low<high)    {        while (low<high && vec[high]>=pivot)        {            high--;        }        vec[low] = vec[high];        while (low <high&&vec[low]<=pivot)        {            low++;        }        vec[high] = vec[low];    }    vec[low] = pivot;    return low;}//使用递归快速排序template<typename Comparable>void quicksort1(vector<Comparable> &vec,int low ,int high){    if (low <high)    {        int mid = partition(vec, low, high);        quicksort1(vec, low, mid - 1);        quicksort1(vec, mid + 1, high);    }}//其实就是用栈保存每一个待排序子串的首尾元素下标，下一次while循环时取出这个范围，对这段子序列进行partition操作,//每次得到的mid都是vector的最终位置，知道栈中不需要放入，也没有数据时，循环结束template<typename Comparable>void quicksort2(vector<Comparable> &vec, int low, int high){    stack<int> st;    if (low<high)    {        int mid = partition(vec, low, high);        if (low<mid-1)        {            st.push(low);            st.push(mid - 1);        }        if (mid+1<high)        {            st.push(mid + 1);            st.push(high);        }        while (!st.empty())        {            int q = st.top();            st.pop();            int p = st.top();            st.pop();            mid = partition(vec, p, q);            if (p<mid-1)            {                st.push(p);                st.push(mid - 1);            }            if (mid+1<q)            {                st.push(mid + 1);                st.push(q);            }        }    }}int _tmain(int argc, _TCHAR* argv[]){    int a[10] = { 12, 21, 33, 4, 50, 62, 71, 52,111,9 };    vector<int> vec(a, a + 10);    int len = vec.size();    //quicksort1(vec, 0, len - 1);    quicksort2(vec, 0, len - 1);    for (int i=0; i < len;i++)    {        cout << vec[i]<< endl;    }    system("pause");    return 0;}`

java代码实现：

package com.bineraytree.test;import java.util.Stack;public class StackTest {    protected static int partition(int arr[],int low,int high) {        int i=low,j=high;        int temp=arr[low];        while(i<j) {            while (i<j&& temp <= arr[j])                --j;            arr[i] = arr[j];            while(i<j && temp >= arr[i])                 ++i;            arr[j] = arr[i];        }        arr[i] = temp;        return i;    }    //递归排序    public static void quickSort1(int arr[],int low,int high){        if(low < high) {            int mid = partition(arr, low, high);            quickSort1(arr, low, mid-1);            quickSort1(arr, mid+1, high);        }    }    //非递归实现    public static void quickSort2(int arr[],int low,int high) {        Stack<Integer> st = new Stack<Integer>();        if (low < high) {            int mid = partition(arr, low, high);            if (mid-1 > low) {                st.push(mid-1);                st.push(low);            }            if (mid+1 < high) {                st.push(high);                st.push(mid+1);            }            while (!st.isEmpty()) {                int q_low = st.peek();                st.pop();                int p_high = st.peek();                st.pop();                mid = partition(arr, q_low, p_high);                if (mid-1 > q_low) {                    st.push(mid-1);                    st.push(q_low);                }                if (mid+1 < p_high) {                    st.push(p_high);                    st.push(mid+1);                }            }        }    }    public static void main(String[] args) {        int[] arr = new int[]{10,12,5,8,96,54,36,25,1,258,366};//      Stack<int> stack = new Stack<int>();//      for (int i = 0; i < arr.length; i++) {//          stack.push(arr[i]);//      }//      System.out.println(stack.search(96)+"-------");//      for (int i = 0; i < arr.length; i++) {//          System.out.println(stack.peek()+"this is peek");//          System.out.println(stack.pop()+" is outing!!");//          System.out.println(stack.isEmpty());//      }        quickSort1(arr,0, arr.length-1);//      quickSort2(arr,0, arr.length-1);        for (int i = 0; i < arr.length; i++) {            System.out.println(arr[i]);        }    }}