堆排序 C++

堆排序的的步骤（从小到大）：
1. 先构建最大堆；
2. 维护一个tail，表示堆的底部，即数组中0-tail部分为堆，tail初始为nums.size()-1，tail之后的元素为已排好序的部分；
3. 将堆顶的元素与tail交换，tail减一，然后对堆顶的元素做一次down操作，重复这个步骤，直到tail为0；

#include <iostream>#include <algorithm>#include <string>#include <vector>#include <random>using namespace std;void swap(vector<int>& nums, int i, int j){    int temp = nums[i];    nums[i] = nums[j];    nums[j] = temp;}void up(vector<int>& nums, int i){    int father = (i - 1) / 2;    if (i > 0 && nums[i] > nums[father])    {        swap(nums, i, father);        up(nums, father);    }}void down(vector<int>& nums, int i, int tail){    int son = i * 2 + 1;    if (son > tail)        return;    if (son + 1 <= tail && nums[son + 1] > nums[son])        ++son;    if (nums[i] < nums[son])    {        swap(nums, i, son);        down(nums, son, tail);    }}void heapSort(vector<int>& nums, int tail){    for (int i = 0; i < nums.size(); ++i)        up(nums, i);    for (int i = nums.size() - 1; i > 0; --i)    {        swap(nums, 0, i);        down(nums, 0, i - 1);    }}int main(){    default_random_engine e;    uniform_int_distribution<int> u(0, 1000);    vector<int> nums(0);    for (int i = 0; i < 20; ++i)        nums.push_back(u(e));    for (int i = 0; i < nums.size(); ++i)        cout << nums[i] << " ";    cout << endl;    heapSort(nums, nums.size() - 1);    for (int i = 0; i < nums.size(); ++i)        cout << nums[i] << " ";    cout << endl;    return 0;}