Quick Sort (C ++ to achieve)

Quick Sort

To sort the array subscript p from among a set of data to r, we have to select any one of data between p r as the Pivot (partition points). We traverse the data between p r, smaller than the pivot into the left will be greater than the pivot into the right into the middle of the pivot. After this step, the data between the array p r was divided into three portions, between the front p q-1 is less than the pivot, the middle pivot, the latter is between q + 1 to r greater than the pivot. The partition, recursive processing idea, we can use recursive data sorted from the p and subscript index between the q-1 from q + 1 to the data between the r, the interval until reduced to 1, it means that all of the the data are ordered.

The optimal time complexity of O (nlogn)
average time complexity of O (nlogn)
worst time complexity of O (n ^ 2), assuming that the array has been ordered, but we have not yet been set up at the end of the pivot value .

As compared to a merge sort advantages: his time complexity is O (1). So even if it may be degraded worst time complexity to O (n ^ 2), people still tend to use algorithms, but now people have developed a number of measures to try to avoid its degradation to O (n ^ 2)

Code:

#include <iostream>
#include <vector>
using namespace std;

int getPartition(vector<int>& nums,int head,int rear)
{
    int value=nums[rear];
    int i=head,j=0,temp=0;
    for(j=head;j<rear;j++)
    {
        if(nums[j]<value)
        {
            temp=nums[j];
            nums[j]=nums[i];
            nums[i]=temp;
            i++;
        }
    }
    temp=nums[rear];
    nums[rear]=nums[i];
    nums[i]=temp;
    return i;
}

void quickSort(vector<int>& nums,int head,int rear)
{
    if(head>=rear)
    {
        return;
    }
    else
    {
        int loc=getPartition(nums,head,rear);
        quickSort(nums,head,loc-1); //注意要是-1而不能这里是loc下一行是加1
        quickSort(nums,loc+1,rear);
    }
}

int main()
{

    vector<int> test;
    test.push_back(5);
    test.push_back(13);
    test.push_back(13);
    test.push_back(7);
    test.push_back(19);
    test.push_back(12);
    test.push_back(4);
    test.push_back(6);
    test.push_back(1);
    test.push_back(2);
    test.push_back(3);
    test.push_back(8);
    for(int i=0;i<test.size();i++)
    {
        cout<<test[i]<<" ";
    }
    cout<<endl;
    int qsize=test.size();
    quickSort(test,0,qsize-1);
    for(int i=0;i<test.size();i++)
    {
        cout<<test[i]<<" ";
    }
    return 0;

}