快速排序

小练手，自写快排，注意函数的引用传递(若采用数组则不必，因vector是一个模板，当采用值传递时将会调用拷贝构造函数生成一个临时类，达不到修改原vector的目的)

若判断key时不带等号，当出现两个同样的值时会导致无限递归(导致stack overflow)

不稳定(示例：6 6 5)，最佳时间复杂度nlogn，最差n^2

#include<iostream>#include<string>#include<vector>using namespace std;void test(vector<int>& vec, int left, int right) {if (left >= right) return;int beg = left, end = right;int key = vec[left];while (left < right){while (left < right && vec[right] >= key)right--;vec[left] = vec[right];while (right > left && vec[left] <= key)left++;vec[right] = vec[left];}vec[left] = key;test(vec, beg, left - 1);test(vec, left + 1, end);}int main(){vector<int> vec = { 3,1,2,4,6,9,8,7,5,0,5 };cout << "排序前:";for (auto i : vec)cout << i << " ";cout << endl;test(vec, 0, vec.size() - 1);cout << "排序后:";for (auto i : vec)cout << i << " ";cout << endl;system("pause");return 0;}