Java版快速排序[不稳定]

原理：分治+递归

复杂度：O(nlgn) - O(nlgn) - O(n^2) - O(1)[平均 - 最好 - 最坏 - 空间复杂度]

栈空间0(lgn) - O(n)

// 固定基准public void quickSort(int[] a, int low, int high) {if (null == a || a.length < 2) {return;}if (low < high) {int mid = partition(a, low, high);quickSort(a, low, mid-1);quickSort(a, mid+1, high);}}private int partition(int[] a, int low, int high) {int pivot = a[low];while (low < high) {// 注意等于，否则死循环while (low < high && a[high] >= pivot) {high--;}a[low] = a[high];// 注意等于，否则死循环while (low < high && a[low] <= pivot) {low++;}a[high] = a[low];}a[low] = pivot;return low;}