【经典】【排序】快速排序算法、堆排序

来源：脑客爱刷题

快速排序：

本算法主要改进了快排的partition算法，使得每次partition后，等于target的数在未排序部分的“中间”连续出现，target左边部分比它小，右边部分比它大。

void partition(vector<int> &num, int begin, int end){if (begin >= end)return;int smaller = begin - 1, bigger = end + 1, cur = begin + 1, target = num[begin];while (cur != bigger){if (num[cur] == target){cur++;}else if (num[cur] < target){swap(num[cur], num[smaller + 1]);smaller++;cur++;}else{swap(num[cur], num[bigger - 1]);bigger--;}}partition(num, begin, smaller);partition(num, bigger, end);}void quicksort(vector<int> &num){if (num.size() <= 1)return;partition(num, 0, num.size() - 1);}

堆排序：

//数组[0,index-1]的范围内都是已经建成的最大堆，现在要把num[index]加入堆中void heapInsert(vector<int> &num, int index){while (index != 0){int parent = (index - 1) / 2;if (num[parent] < num[index])swap(num[parent], num[index]);elsebreak;index = parent;}}//num[0]不在堆的正确位置，把它往下“沉”，直到正确位置为止，堆的范围是[0,size-1]void heapDown(vector<int> &num, int size){int index = 0, largest = index, left = index * 2 + 1, right = index * 2 + 2;while (left < size){if (num[left] > num[largest])largest = left;if (right<size && num[right] > num[largest])largest = right;if (largest != index){swap(num[largest], num[index]);index = largest;left = index * 2 + 1;right = index * 2 + 2;}elsebreak;}}void heapsort(vector<int> &num){if (num.size() <= 1)return;for (int i = 1; i < num.size(); i++){heapInsert(num, i);//建立最大堆}for (int i = num.size() - 1; i >= 1; i--){swap(num[0], num[i]);heapDown(num, i);}}