快速排序

https://blog.csdn.net/nrsc272420199/article/details/82587933
理论基础在上文链接

代码实现

#include
using namespace std;
int a[100] = { 5,33,3,7,11,6,8,100 };

void quickSort(int a[],int start,int end) {
    if (start >= end) 
        return;
    int i = start, j = end;
    int temp = a[start];
    bool flag = 0;  //0时end从后往前扫描，1时start从前往后扫描
    while (start != end) {
        if (flag == 0) {    //0时end从后往前扫描
            if (a[end] > temp) {
                end--;
            }
            else
            {
                a[start] = a[end];
                start++;
                flag = 1;
            }
        }
        else  //1时start从前往后扫描
        {
            if (a[start] < temp) {
                start++;
            }
            else {
                a[end] = a[start];
                end--;
                flag = 0;
            }
        }
        
    }
    a[start] = temp;
    quickSort(a, i, start - 1);
    quickSort(a, start + 1, j);
}

/*
非递归（栈）实现快排
*/
struct node {
    int start;
    int end;
};

void quickSort_2(int a[], int start, int end) {
    stack st;
    node *no = new node; 
    no->start = start;
    no->end = end;
    st.push(no);
    while (!st.empty()){
        start = st.top()->start;
        end = st.top()->end;
        if (start >= end)
            return;
        int i = start, j = end;
        int temp = a[start];
        bool flag = 0;  //0时end从后往前扫描，1时start从前往后扫描
        while (start != end) {
            if (flag == 0) {    //0时end从后往前扫描
                if (a[end] > temp) {
                    end--;
                }
                else
                {
                    a[start] = a[end];
                    start++;
                    flag = 1;
                }
            }
            else  //1时start从前往后扫描
            {
                if (a[start] < temp) {
                    start++;
                }
                else {
                    a[end] = a[start];
                    end--;
                    flag = 0;
                }
            }

        }
        a[start] = temp;
        st.pop();
        no->start = i;
        no->end = start - 1;
        st.push(no);

        no->start = start + 1;
        no->end = j;
        st.push(no);
    }
    
}

int main() {
    int len = 8;
    quickSort(a, 0, 7);
    for (int i = 0; i < len; i++) cout << a[i] << " ";
    return 0;
}