输入一个字符串，打印出该字符串中字符的所有排列。例如：输入字符串abc，则打印出由字符a、b、c所能排列出来的所有字符串abc、acb、bac、bca、cab、cba。
这里需要注意的是防止重复的问题，所以需要使用Set来进行过滤，一个for循环就可以搞定,具体代码如下：
package com.example.demo.upload.controller;
import java.util.HashSet;
import java.util.Set;
public class test {
static Set<String> set=new HashSet<>();
public static void main(String[] args) {
String test="abcde";
permutation(test);
for(String str:set){
System.out.println(str);
}
}
public static void permutation(String test){
if (test==null)
return;
permutationtest(test.toCharArray(),0);
}
public static void permutationtest(char[] chars,int pos){
if (pos==chars.length-1){
if (!set.contains(chars.toString())){
set.add(String.valueOf(chars));
}
}
for (int i=pos;i<chars.length;i++){
char temp=chars[i];
chars[i]=chars[pos];
chars[pos]=temp;
permutationtest(chars,pos+1);
temp=chars[i];
chars[i]=chars[pos];
chars[pos]=temp;
}
}
}
返回结果如下：
D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\bin\java.exe "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2018.2.5\lib\idea_rt.jar=53214:C:\Program Files\JetBrains\IntelliJ IDEA 2018.2.5\bin" -Dfile.encoding=UTF-8 -classpath D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\charsets.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\deploy.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\access-bridge-64.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\cldrdata.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\dnsns.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\jaccess.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\jfxrt.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\localedata.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\nashorn.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\sunec.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\sunjce_provider.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\sunmscapi.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\sunpkcs11.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\ext\zipfs.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\javaws.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\jce.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\jfr.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\jfxswt.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\jsse.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\management-agent.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\plugin.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\resources.jar;D:\sofeware\jdk1.8\JDK1.8\Java\jdk1.8.0_301\jre\lib\rt.jar;D:\project\fenpian\FragmentUpload-master\target\classes;C:\Users\ligx1\.m2\repository\org\springframework\boot\spring-boot-starter-thymeleaf\2.3.1.RELEASE\spring-boot-starter-thymeleaf-2.3.1.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\boot\spring-boot-starter\2.3.1.RELEASE\spring-boot-starter-2.3.1.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\boot\spring-boot\2.3.1.RELEASE\spring-boot-2.3.1.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\boot\spring-boot-starter-logging\2.3.1.RELEASE\spring-boot-starter-logging-2.3.1.RELEASE.jar;C:\Users\ligx1\.m2\repository\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;C:\Users\ligx1\.m2\repository\ch\qos\logback\logback-core\1.2.3\logback-core-1.2.3.jar;C:\Users\ligx1\.m2\repository\org\apache\logging\log4j\log4j-to-slf4j\2.13.3\log4j-to-slf4j-2.13.3.jar;C:\Users\ligx1\.m2\repository\org\apache\logging\log4j\log4j-api\2.13.3\log4j-api-2.13.3.jar;C:\Users\ligx1\.m2\repository\org\slf4j\jul-to-slf4j\1.7.30\jul-to-slf4j-1.7.30.jar;C:\Users\ligx1\.m2\repository\jakarta\annotation\jakarta.annotation-api\1.3.5\jakarta.annotation-api-1.3.5.jar;C:\Users\ligx1\.m2\repository\org\yaml\snakeyaml\1.26\snakeyaml-1.26.jar;C:\Users\ligx1\.m2\repository\org\thymeleaf\thymeleaf-spring5\3.0.11.RELEASE\thymeleaf-spring5-3.0.11.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\thymeleaf\thymeleaf\3.0.11.RELEASE\thymeleaf-3.0.11.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\attoparser\attoparser\2.0.5.RELEASE\attoparser-2.0.5.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\unbescape\unbescape\1.1.6.RELEASE\unbescape-1.1.6.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\slf4j\slf4j-api\1.7.30\slf4j-api-1.7.30.jar;C:\Users\ligx1\.m2\repository\org\thymeleaf\extras\thymeleaf-extras-java8time\3.0.4.RELEASE\thymeleaf-extras-java8time-3.0.4.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\boot\spring-boot-starter-web\2.3.1.RELEASE\spring-boot-starter-web-2.3.1.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\boot\spring-boot-starter-json\2.3.1.RELEASE\spring-boot-starter-json-2.3.1.RELEASE.jar;C:\Users\ligx1\.m2\repository\com\fasterxml\jackson\core\jackson-databind\2.11.0\jackson-databind-2.11.0.jar;C:\Users\ligx1\.m2\repository\com\fasterxml\jackson\core\jackson-annotations\2.11.0\jackson-annotations-2.11.0.jar;C:\Users\ligx1\.m2\repository\com\fasterxml\jackson\core\jackson-core\2.11.0\jackson-core-2.11.0.jar;C:\Users\ligx1\.m2\repository\com\fasterxml\jackson\datatype\jackson-datatype-jdk8\2.11.0\jackson-datatype-jdk8-2.11.0.jar;C:\Users\ligx1\.m2\repository\com\fasterxml\jackson\datatype\jackson-datatype-jsr310\2.11.0\jackson-datatype-jsr310-2.11.0.jar;C:\Users\ligx1\.m2\repository\com\fasterxml\jackson\module\jackson-module-parameter-names\2.11.0\jackson-module-parameter-names-2.11.0.jar;C:\Users\ligx1\.m2\repository\org\springframework\boot\spring-boot-starter-tomcat\2.3.1.RELEASE\spring-boot-starter-tomcat-2.3.1.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\apache\tomcat\embed\tomcat-embed-core\9.0.36\tomcat-embed-core-9.0.36.jar;C:\Users\ligx1\.m2\repository\org\glassfish\jakarta.el\3.0.3\jakarta.el-3.0.3.jar;C:\Users\ligx1\.m2\repository\org\apache\tomcat\embed\tomcat-embed-websocket\9.0.36\tomcat-embed-websocket-9.0.36.jar;C:\Users\ligx1\.m2\repository\org\springframework\spring-web\5.2.7.RELEASE\spring-web-5.2.7.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\spring-beans\5.2.7.RELEASE\spring-beans-5.2.7.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\spring-webmvc\5.2.7.RELEASE\spring-webmvc-5.2.7.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\spring-aop\5.2.7.RELEASE\spring-aop-5.2.7.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\spring-context\5.2.7.RELEASE\spring-context-5.2.7.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\spring-expression\5.2.7.RELEASE\spring-expression-5.2.7.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\spring-core\5.2.7.RELEASE\spring-core-5.2.7.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\spring-jcl\5.2.7.RELEASE\spring-jcl-5.2.7.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\projectlombok\lombok\1.18.12\lombok-1.18.12.jar;C:\Users\ligx1\.m2\repository\commons-io\commons-io\2.4\commons-io-2.4.jar;C:\Users\ligx1\.m2\repository\commons-fileupload\commons-fileupload\1.3.3\commons-fileupload-1.3.3.jar;C:\Users\ligx1\.m2\repository\mysql\mysql-connector-java\8.0.22\mysql-connector-java-8.0.22.jar;C:\Users\ligx1\.m2\repository\com\baomidou\mybatis-plus-boot-starter\3.3.2\mybatis-plus-boot-starter-3.3.2.jar;C:\Users\ligx1\.m2\repository\com\baomidou\mybatis-plus\3.3.2\mybatis-plus-3.3.2.jar;C:\Users\ligx1\.m2\repository\com\baomidou\mybatis-plus-extension\3.3.2\mybatis-plus-extension-3.3.2.jar;C:\Users\ligx1\.m2\repository\com\baomidou\mybatis-plus-core\3.3.2\mybatis-plus-core-3.3.2.jar;C:\Users\ligx1\.m2\repository\com\baomidou\mybatis-plus-annotation\3.3.2\mybatis-plus-annotation-3.3.2.jar;C:\Users\ligx1\.m2\repository\com\github\jsqlparser\jsqlparser\3.1\jsqlparser-3.1.jar;C:\Users\ligx1\.m2\repository\org\mybatis\mybatis\3.5.4\mybatis-3.5.4.jar;C:\Users\ligx1\.m2\repository\org\mybatis\mybatis-spring\2.0.4\mybatis-spring-2.0.4.jar;C:\Users\ligx1\.m2\repository\org\springframework\boot\spring-boot-autoconfigure\2.3.1.RELEASE\spring-boot-autoconfigure-2.3.1.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\boot\spring-boot-starter-jdbc\2.3.1.RELEASE\spring-boot-starter-jdbc-2.3.1.RELEASE.jar;C:\Users\ligx1\.m2\repository\com\zaxxer\HikariCP\3.4.5\HikariCP-3.4.5.jar;C:\Users\ligx1\.m2\repository\org\springframework\spring-jdbc\5.2.7.RELEASE\spring-jdbc-5.2.7.RELEASE.jar;C:\Users\ligx1\.m2\repository\org\springframework\spring-tx\5.2.7.RELEASE\spring-tx-5.2.7.RELEASE.jar com.example.demo.upload.controller.test
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Process finished with exit code 0
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