quicksort 快速排序 quick sort
* Java基本版
package cn.mediamix;
import java.util.LinkedList;
public class QuickSort {
public static void qsort(int[]a) {
_qsort(a, 0, a.length-1);
}
private static void _qsort(int []a, int low, int high) {
if (low >= high) {
return;
}
int first = low, last = high, pivot = a[first];
while (first < last) {
while (first < last && a[last] >= pivot) {
--last;
}
a[first] = a[last];
while (first < last && pivot >= a[first]) {
++first;
}
a[last] = a[first];
}
a[first] = pivot;
_qsort(a, low, first-1);
_qsort(a, first+1, high);
}
public static void main(String[] args) {
int[] a = {9, 1, 4, 7, 8, 0, 6, 5, 2, 3};
qsort(a);
// 测试新的遍历方式
LinkedList<Integer> items = new LinkedList<Integer>();
for (int e : a) {
items.add(new Integer(e));
}
items.forEach(item->System.out.println(item));
}
}
* Java通用版排序
GenericSort.java
package cn.mediamix;
import java.util.Comparator;
import java.util.List;
public class GenericSort<T> {
public static <T> void qsort(List<T> a, Comparator<T> comparator) {
_qsort(a, 0, a.size() - 1, comparator);
}
private static <T> void _qsort(List<T> a, int low, int high, Comparator<T> comparator) {
if (low >= high) {
return;
}
int first = low, last = high;
T pivot = a.get(first);
while (first < last) {
while (first < last && comparator.compare(a.get(last), pivot) >= 0) {
--last;
}
a.set(first, a.get(last));
while (first < last && comparator.compare(pivot, a.get(first)) >= 0) {
++first;
}
a.set(last, a.get(first));
}
a.set(first, pivot);
_qsort(a, low, first - 1, comparator);
_qsort(a, first + 1, high, comparator);
}
}
TestGeneric.java
package cn.mediamix;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;
import cn.mediamix.GenericSort;
public class TestGeneric {
public static void main(String[] args) {
int[] a = {9, 1, 4, 7, 8, 0, 6, 5, 2, 3};
// int[] => List<Integer>
List<Integer> items = new ArrayList<Integer>(a.length);
for (int e : a) {
items.add(new Integer(e));
}
// my qsort
GenericSort.qsort(items, new Comparator<Integer>() {
@Override
public int compare(Integer i1, Integer i2) {
return i2-i1; // 从大到小排序
}
});
// traverse
items.forEach(item -> {System.out.println(item);});
// test string
List<String> greet = new LinkedList<String>();
greet.add("Hello");
greet.add("Bonjour");
greet.add("Shalom");
greet.add("Hola");
greet.add("Konnichiwa");
greet.add("Nihao");
GenericSort.qsort(greet, new Comparator<String>() {
@Override
public int compare(String s1, String s2) {
return s1.compareTo(s2);
}
});
greet.forEach(item -> {System.out.println(item);});
}
}
Output:
9 8 7 6 5 4 3 2 1 0 Bonjour Hello Hola Konnichiwa Nihao Shalom
参考代码片段
Collections.sort(list, new Comparator<Dog>() { @Override public int compare(Dog o1, Dog o2) { return o2.age - o1.age; } });
@file: java.util.collections
public class Collections {
// ...
public static <T> void sort(List<T> list, Comparator<? super T> c) {
list.sort(c);
}
//...
}
@file: java.util.List
public interface List<E> extends Collection<E> {
// ...
@SuppressWarnings({"unchecked", "rawtypes"})
default void sort(Comparator<? super E> c) {
Object[] a = this.toArray();
Arrays.sort(a, (Comparator) c);
ListIterator<E> i = this.listIterator();
for (Object e : a) {
i.next();
i.set((E) e);
}
}
// ...
}
@file: java.util.comparator
public interface Comparator<T> {
// ...
int compare(T o1, T o2);
}
//-------------------------------------------------------------------------//
// 下面的是弱类型的脚本语言: //
// ----------------------------------------------------------------------------------------//
* javascript
// 上一次写错了 first < last 对于下标比较大小，控制下标走动位置，不需要用比较大小的回调函数
/**
* Created by Mch on 8/5/18.
*/
function qsort(a, c) {
c = c || function(a, b) {
return a - b;
};
function _qsort(a, low, high) {
if (low >= high) {
return;
}
var first = low, last = high, pivot = a[first];
while (first < last) {
while (first < last && c(a[last], pivot) >= 0) {
--last;
}
a[first] = a[last];
while (first < last && c(pivot, a[first]) >= 0) {
++first;
}
a[last] = a[first];
}
a[first] = pivot;
_qsort(a, low, first-1);
_qsort(a, first+1, high);
}
return _qsort(a, 0, a.length-1);
}
test:
var a = [9, 1, 4, 7, 8, 0, 6, 5, 2, 3];
qsort(a, function(a, b) {
return b-a;
});
console.log(a);
var b = ['Hello', 'wold', 'sange', 'yasha', 'shuriken', 'sword'];
qsort(b, function(a, b) {
return a.localeCompare(b);
});
console.log(b);
output:
[ 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 ] [ 'Hello', 'sange', 'shuriken', 'sword', 'wold', 'yasha' ]
* PHP:
http://php.net/manual/en/function.usort.php
bool usort ( array &$array , callable $value_compare_func )
<?php
class QuickSort {
private $compare;
public function __construct($compare) {
if (!$compare) {
$compare = function($a, $b) {
return $a - $b;
};
}
$this->compare = $compare;
}
private function _qsort(&$a, $low, $high) {
if ($low >= $high) {
return;
}
$first = $low;
$last = $high;
$pivot = $a[$first];
$c = $this->compare;
$ge = function($a, $b) use ($c) {
return call_user_func($c, $a, $b) >= 0;
};
while ($first < $last) {
while ($first < $last && $ge($a[$last], $pivot)) {
--$last;
}
$a[$first] = $a[$last];
while ($first < $last && $ge($pivot, $a[$first])) {
++$first;
}
$a[$last] = $a[$first];
}
$a[$first] = $pivot;
self::_qsort($a, $low, $first-1);
self::_qsort($a, $first+1, $high);
}
public function qsort(&$a) {
self::_qsort($a, 0, count($a)-1);
}
}
test:
<?php
// test: "Hello world Blog Control" 字符串按空格分隔，分成数组，转化为小写，按字母顺序排
$a = explode(" ", "Hello world Blog Control");
$a = array_map(function($e) {
return strtolower($e);
}, $a);
$q = new QuickSort(function($a, $b) {
return strcmp($a, $b);
});
$q->qsort($a); // 这里用call_user_func($q->qsort, $a)不起作用?
print_r($a);
Output:
Array
(
[0] => blog
[1] => control
[2] => hello
[3] => world
)
快速排序算法
