思路 基于荷兰国旗问题的思想,将数组划分为3部分,分别是:小于num,等于num,大于num。对小于num和大于num的部分递归求解。其中num取每个区域的最后一个值。
时间复杂度O(N*logN),额外空间复杂度O(logN)
package section1;
import java.util.Arrays;
public class QuickSort {
public static void quickSort(int[] arr){
if (arr == null || arr.length < 2) return;
sort(arr, 0, arr.length-1);
}
public static void sort(int[] arr, int L, int R){
if (L < R){
int fl = L - 1;
int fr = R;
for (int i = L; i < fr; i++){
if (arr[i] < arr[R]) change(arr, i, ++fl);
else if (arr[i] == arr[R]) continue;
else change(arr, i--, --fr);
}
change(arr, fr, R); // 记得将用作比较的最后一个值与big区的第一个数交换
sort(arr, L, fl);
sort(arr, fr, R);
}
}
public static int[] partation(int[] arr, int L, int R){
int fl = L - 1;
int fr = R;
for (int i = L; i < fr; i++){
if (arr[i] < arr[R]) change(arr, i, ++fl);
else if (arr[i] == arr[R]) continue;
else change(arr, i--, --fr);
}
change(arr, fr, R);
return new int[] {fl + 1, fr};
}
public static void change(int[] arr, int a, int b){
int f = arr[a];
arr[a] = arr[b];
arr[b] = f;
}
// for test
public static void comparator(int[] arr) {
Arrays.sort(arr);
}
// for test
public static int[] generateRandomArray(int maxSize, int maxValue) {
int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
for (int i = 0; i < arr.length; i++) {
arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
}
return arr;
}
// for test
public static int[] copyArray(int[] arr) {
if (arr == null) {
return null;
}
int[] res = new int[arr.length];
for (int i = 0; i < arr.length; i++) {
res[i] = arr[i];
}
return res;
}
// for test
public static boolean isEqual(int[] arr1, int[] arr2) {
if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
return false;
}
if (arr1 == null && arr2 == null) {
return true;
}
if (arr1.length != arr2.length) {
return false;
}
for (int i = 0; i < arr1.length; i++) {
if (arr1[i] != arr2[i]) {
return false;
}
}
return true;
}
// for test
public static void printArray(int[] arr) {
if (arr == null) {
return;
}
for (int i = 0; i < arr.length; i++) {
System.out.print(arr[i] + " ");
}
System.out.println();
}
// for test
public static void main(String[] args) {
int testTime = 500000;
int maxSize = 100;
int maxValue = 100;
boolean succeed = true;
for (int i = 0; i < testTime; i++) {
int[] arr1 = generateRandomArray(maxSize, maxValue);
int[] arr2 = copyArray(arr1);
quickSort(arr1);
comparator(arr2);
if (!isEqual(arr1, arr2)) {
succeed = false;
printArray(arr1);
printArray(arr2);
break;
}
}
System.out.println(succeed ? "Nice!" : "Fucking fucked!");
int[] arr = generateRandomArray(maxSize, maxValue);
printArray(arr);
quickSort(arr);
printArray(arr);
}
}