思想:分治思想
先排序(找到切分元素,小于此元素的放在前,大于此元素的放在后面)再递归。
1.基本快速排序:
2.二切分:i=low,j=hi+1,辅助元素v=a[low]
package com.mahai.sort;
import java.util.Scanner;
public class Quick {
//TODO 递归第一步
public static void sort(String[] list) {
/**
* 可以添加打乱数组元素功能
*/
sort(list, 0, list.length-1);
}
//TODO 递归第二步
private static void sort(String[] list,int low,int hi) {
if (hi <= low) return;
int j = partition(list, low, hi);//
sort(list, low, j-1);//以j为界限扫描左边元素,并切分排序
sort(list, j+1, hi);
}
//TODO 切分并排序
private static int partition(String[] list,int low,int hi) {
int i = low,j = hi+1;
String v = list[low];
while (true) {
while (less(list[++i], v)) if (i==hi) break;//这块break跳出此处while循环
while (less(v, list[--j])) if (j==low) break;
if (i >= j) break;
exch(list, i, j);
}
exch(list, low, j);
return j;
}
//TODO 比较大小
private static boolean less(String a,String b) {
return a.hashCode()<b.hashCode();
}
//TODO 交换元素
private static void exch(String[] list,int i,int j) {
String ex;
ex = list[i];
list[i] = list[j];
list[j] = ex;
}
//TODO 显示数组
private static void show(String[] list) {
for (int i = 0; i < list.length; i++) {
System.out.print(list[i] + " ");
}
System.out.println();
}
//TODO main方法
public static void main(String[] args) {
Scanner s =new Scanner(System.in);
System.out.println("请输入数组长度:");
int N = s.nextInt();
String[] list =new String[N];
for (int i = 0; i < N; i++) {
System.out.println("请输入第"+(i+1)+"个数组元素:");
list[i] = s.next();
}
s.close();
System.out.println("输入完毕!");
show(list);
sort(list);
show(list);
}
}
3.三切分:切分元素为相同元素,lt = low,i = low+1,gt = hi,辅助元素v=a[low]
package com.mahai.sort;
import java.util.Scanner;
public class Quick3way {
//TODO 三向切分
@SuppressWarnings({ "unchecked", "rawtypes" })
public static void sort(Comparable[] a,int low,int hi) {
if (hi <= low) return;
int lt = low,i = low+1,gt = hi;
Comparable v = a[low];
while (i <= gt) {
int com = a[i].compareTo(v);
if (com < 0) exch(a, lt++, i++);
else if (com > 0) exch(a,gt--,i++);
else i++;
}
sort(a, low, lt-1);
sort(a, gt+1, hi);
}
// TODO 交换元素
@SuppressWarnings("rawtypes")
private static void exch(Comparable[] a, int i, int j) {
Comparable ex;
ex = a[i];
a[i] = a[j];
a[j] = ex;
}
// TODO 显示数组
@SuppressWarnings("rawtypes")
private static void show(Comparable[] a) {
for (int i = 0; i < a.length; i++) {
System.out.print(a[i] + " ");
}
System.out.println();
}
// TODO main方法
@SuppressWarnings("rawtypes")
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.println("请输入数组长度:");
int N = s.nextInt();
Comparable[] a = new Comparable[N];
for (int i = 0; i < N; i++) {
System.out.println("请输入第" + (i + 1) + "个数组元素:");
a[i] = s.next();
}
s.close();
System.out.println("输入完毕!");
show(a);
sort(a,0,a.length-1);
show(a);
}
}