参考：https://zh.wikipedia.org/wiki/%E5%BF%AB%E9%80%9F%E6%8E%92%E5%BA%8F#Java
public static void qSort(int[] arr, int head, int tail) {
if (head >= tail || arr == null || arr.length <= 1) {
return;
}
int i = head, j = tail, pivot = arr[(head + tail) / 2];
while (i <= j) {
while (arr[i] < pivot) {
++i;
}
while (arr[j] > pivot) {
--j;
}
if (i < j) {
int t = arr[i];
arr[i] = arr[j];
arr[j] = t;
++i;
--j;
} else if (i == j) {
++i;
}
}
qSort(arr, head, j);
qSort(arr, i, tail);
}
public static void main(String[] args) {
int[] arr = new int[]{1, 4, 8, 2, 55, 3, 4, 8, 6, 4, 0, 11, 34, 90, 23, 54, 77, 9, 2, 9, 4, 10};
qSort(arr, 0, arr.length - 1);
String out = "";
for (int digit : arr) {
out += (digit + ",");
}
System.out.println(out);
}