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算法-十大经典排序算法
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Diff for: ‎Algorithm/.gitignore

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target/
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!.mvn/wrapper/maven-wrapper.jar
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!**/src/main/**/target/
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!**/src/test/**/target/
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### STS ###
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.apt_generated
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.classpath
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.factorypath
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.project
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.settings
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.springBeans
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.sts4-cache
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### IntelliJ IDEA ###
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.idea
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*.iws
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*.iml
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*.ipr
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### NetBeans ###
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/nbproject/private/
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/nbbuild/
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/dist/
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/nbdist/
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/.nb-gradle/
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build/
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!**/src/main/**/build/
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!**/src/test/**/build/
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### VS Code ###
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.vscode/

Diff for: ‎Algorithm/HELP.md

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# Getting Started
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### Reference Documentation
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For further reference, please consider the following sections:
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* [Official Apache Maven documentation](https://maven.apache.org/guides/index.html)
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* [Spring Boot Maven Plugin Reference Guide](https://docs.spring.io/spring-boot/docs/2.7.5/maven-plugin/reference/html/)
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* [Create an OCI image](https://docs.spring.io/spring-boot/docs/2.7.5/maven-plugin/reference/html/#build-image)
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* [Spring Boot DevTools](https://docs.spring.io/spring-boot/docs/2.7.5/reference/htmlsingle/#using.devtools)
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Diff for: ‎Algorithm/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-parent</artifactId>
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<version>2.7.5</version>
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<relativePath/> <!-- lookup parent from repository -->
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</parent>
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<groupId>com.algorithm</groupId>
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<artifactId>Algorithm</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<name>Algorithm</name>
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<description>Demo project for Spring Boot</description>
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<properties>
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<java.version>1.8</java.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter</artifactId>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-devtools</artifactId>
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<scope>runtime</scope>
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<optional>true</optional>
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</dependency>
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<dependency>
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<groupId>org.projectlombok</groupId>
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<artifactId>lombok</artifactId>
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<optional>true</optional>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-test</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-maven-plugin</artifactId>
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<configuration>
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<excludes>
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<exclude>
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<groupId>org.projectlombok</groupId>
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<artifactId>lombok</artifactId>
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</exclude>
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</excludes>
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</configuration>
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</plugin>
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</plugins>
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</build>
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</project>

Diff for: ‎Algorithm/src/main/java/com/algorithm/AlgorithmApplication.java

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package com.algorithm;
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import org.springframework.boot.SpringApplication;
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import org.springframework.boot.autoconfigure.SpringBootApplication;
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/**
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* 算法
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*
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* @author wliduo[[email protected]]
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* @date 2022/11/22 9:52
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*/
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@SpringBootApplication
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public class AlgorithmApplication {
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public static void main(String[] args) {
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SpringApplication.run(AlgorithmApplication.class, args);
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}
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}

Diff for: ‎Algorithm/src/main/java/com/algorithm/sort/BubbleSort.java

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package com.algorithm.sort;
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import java.util.Arrays;
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/**
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* 冒泡排序
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*
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* 比较相邻的元素。如果第一个比第二个大（小），就交换他们两个
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* 对每一对相邻元素作同样的工作，从开始第一对到结尾的最后一对
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* 这步做完后，最后的元素会是最大（小）的数
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* 针对所有的元素重复以上的步骤，除了最后一个
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*
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* 时间复杂度
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*
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* @author wliduo[[email protected]]
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* @date 2022/11/22 9:52
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*/
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public class BubbleSort {
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/**
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* 冒泡排序算法
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*
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* @param args
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*/
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public static void main(String[] args) {
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int[] array = {5, 3, 2, 4, 9, 8, 7, 1, 6};
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System.out.println("---------- bubbleSort1 ----------");
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bubbleSort1(Arrays.copyOf(array, array.length));
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System.out.println("---------- bubbleSort2 ----------");
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bubbleSort2(Arrays.copyOf(array, array.length));
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System.out.println("---------- bubbleSort3 ----------");
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bubbleSort3(Arrays.copyOf(array, array.length));
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System.out.println("---------- bubbleSort4 ----------");
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int[] array4 = {4, 1, 2, 3, 9, 8, 7, 5, 6};
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bubbleSort4(Arrays.copyOf(array4, array.length));
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}
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/**
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* 先写出一轮的冒泡排序处理，冒泡一样的交换位置到最后一位
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*
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* 大于就交换位置是从小到大，每次大于后面的值才交换，最后一位是最大值
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* 小于就交换位置是从大到小，每次小于后面的值才交换，最后一位是最小值
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*
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* array.length - 1，不然会超出边界，因为 array[j + 1]
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*
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* 当然也可以是从j = 1开始，j和j - 1进行比较，这样就不用array.length - 1了
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* 大于和小于也需要调换，大于会变成从大到小，小于会变成从小到大
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* 当然这种逆向的理解起来比较复杂一点，第二块代码是逆向的写法
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*
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* @param array
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*/
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private static void bubbleSort1(int[] array) {
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print(array);
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for (int j = 0; j < array.length - 1; j++) {
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if (array[j] > array[j + 1]) {
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int temp = array[j];
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array[j] = array[j + 1];
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array[j + 1] = temp;
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}
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}
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/*for (int j = 1; j < array.length; j++) {
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if (array[j] < array[j - 1]) {
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int temp = array[j];
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array[j] = array[j - 1];
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array[j - 1] = temp;
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}
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}*/
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print(array);
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}
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/**
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* 基于一轮的冒泡排序处理，再增加一个外循环
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* 将每个位置的数字都进行一轮冒泡交换
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* 这样一个最基础的冒泡排序就完成了
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*
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* 给定一个count记录循环次数
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*
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* @param array
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*/
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private static void bubbleSort2(int[] array) {
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print(array);
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// count记录循环次数
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int count = 0;
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for (int i = 0; i < array.length; i++) {
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for (int j = 0; j < array.length - 1; j++) {
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count++;
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if (array[j] > array[j + 1]) {
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int temp = array[j];
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array[j] = array[j + 1];
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array[j + 1] = temp;
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}
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}
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}
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System.out.println("count: " + count);
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print(array);
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}
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/**
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* 优化版本，内循环减去i就行了
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* 每次冒泡后到i位置的数字都已经排序好了
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* 所以就没必要重复排
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*
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* 可以看到count次数少了一半
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*
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* @param array
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*/
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private static void bubbleSort3(int[] array) {
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print(array);
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// count记录循环次数
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int count = 0;
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for (int i = 0; i < array.length; i++) {
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for (int j = 0; j < array.length - i - 1; j++) {
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if (array[j] > array[j + 1]) {
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int temp = array[j];
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array[j] = array[j + 1];
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array[j + 1] = temp;
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}
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count++;
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}
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}
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// 还有一种外循环i反过来循环的，意思差不多，就是逆向的
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/*for (int i = array.length - 1; i > 0 ; i--) {
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for (int j = 0; j < i; j++) {
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count++;
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if (array[j] > array[j + 1]) {
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int temp = array[j];
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array[j] = array[j + 1];
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array[j + 1] = temp;
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}
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}
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}*/
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System.out.println("count: " + count);
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print(array);
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}
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/**
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* 优化版本v2，假定数组某些数已经有序
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* 在每轮交换处理可以定一个标记，如果这轮比较都没有交换位置的话
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* 说明数据已经有序，可以直接结束
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*
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* 给定一个count记录循环次数
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* 换一个存在某些数有序的数组，可以看到count次数又会变少
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*
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* @param array
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*/
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private static void bubbleSort4(int[] array) {
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print(array);
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// count记录循环次数
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int count = 0;
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for (int i = 0; i < array.length; i++) {
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// 设定一个标记
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boolean mark = Boolean.TRUE;
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for (int j = 0; j < array.length - i - 1; j++) {
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if (array[j] > array[j + 1]) {
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int temp = array[j];
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array[j] = array[j + 1];
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array[j + 1] = temp;
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mark = Boolean.FALSE;
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}
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count++;
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}
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// 若为true，则表示此次循环没有进行交换
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if (mark) {
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// 也就是待排序列已经有序，排序已经完成，直接结束
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break;
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}
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}
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System.out.println("count: " + count);
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print(array);
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}
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/**
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* 打印数组
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*
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* @param array
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*/
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private static void print(int[] array) {
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for (int i = 0; i < array.length; i++) {
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System.out.print(array[i] + " ");
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}
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System.out.println();
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}
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}

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