教你一步一步写快速排序

快速排序，顾名思义，在各种排序算法中，快速排序算法综合性能最为优异。所以掌握快速排序是一个程序员的基本功。

首先写出我的实现思路，本文采用Java语言，C/C++代码类似：

Step 0 : thinking

public class quickSortDemo{

    public static void main(String args[]){

        //define a test array

        //invoke the quickSort()

        //print the array after it was sorted

    }

    //function quickSort()

    public void quickSort(int array[],int left,int right){

        //do nothing if left >= right

        //invoke the partition()

        //recursive quickSort() the left parts and right parts

    } 

    //function partition()

    public int partition(int array[],int left,int right){

        //p<-get a number from array

        //put elements <= p to the left side

        //put elements >= p to the right side

        //put p in the middle slot which index id pivot

    }

}

Step 1 : encoding

 public int partition(int array[],int left,int right){

        //p<-get a number from array

        int p = array[left];

        int i = left;

        int j = 0;

        for(j=i+1;j<=right;j++){

        //put elements <= p to the left side 

        //put elements >= p to the right side

        if(p>array[j]){

                i++;

                swap(array,i,j);

            }

        }

        //put p in the middle slot which index id pivot

        swap(array,i,left);

        return i;

    }

    public void quickSort(int array[],int left,int right){

               //do nothing if left >= right

if(left<right){

               //invoke the partition()

int pivot = partition(array,left,right);

               //recursive quickSort() the left parts and right parts

quickSort(array,left,pivot-1);

quickSort(array,pivot+1,right);

}

}

Step 2 : add function swap()

//it's main function is to exchange number

public void swap(int array[],int i,int j){

int temp = array[i];

array[i] = array[j];

array[j] = temp;

}

Step 3 : test the class

public class Demo{

public static void main(String args[]){

int temp[] = {3,8,6,4,5,6,1,9,2,0,22,22,22,33,454,5,4,3333,22222};

new Demo().quickSort(temp,0,temp.length-1);

for(int i=0;i<temp.length;i++){

System.out.print(temp[i]+"、");

}

System.out.println();

}