有26个字母a~z，找出所有字母组合，a、b、c、ab、abc、a~z 都是一个组合(顺序无关)

1.*这个问题有点像小学课本上握手问题，每个人都握到最后那个人，这样也就好理解点了
2.*我们可以通过循环加上字符串拼接每次加一个字母，然后存储到数组中，好比：a,a+b,a+b+c,a+b+c+d等等，到了b就清空继续这个操作
*3.*这样一看我们可以采用双重for循环一个负责首字母一个负责后续的拼接

public class ABC {
  public static void main(String[] args) {
    ArrayList list = new ArrayList();
    for (char i = 'a'; i <= 'z'; i++) {
      //清空
      String st = "";
      for (char j = i; j <= 'z'; j++) {
        //拼接
        st += j;
        //存储
        list.add(st);
      }
    }
    //遍历出来所有的组合
    for (String string : list) {
      System.out.println(string);
    }
  }
}

 

D:\develop\JDK1.8\jdk1.8.0_281\bin\java.exe "-javaagent:D:\develop\IntelliJ IDEA 2020.3.2\lib\idea_rt.jar=6168:D:\develop\IntelliJ IDEA 2020.3.2\bin" -Dfile.encoding=UTF-8 -classpath D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\charsets.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\deploy.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\access-bridge-64.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\cldrdata.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\dnsns.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\jaccess.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\jfxrt.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\localedata.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\nashorn.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\sunec.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\sunjce_provider.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\sunmscapi.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\sunpkcs11.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\ext\zipfs.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\javaws.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\jce.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\jfr.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\jfxswt.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\jsse.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\management-agent.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\plugin.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\resources.jar;D:\develop\JDK1.8\jdk1.8.0_281\jre\lib\rt.jar;D:\JavaCode\JavaSE_Code\out\production\Idea_test;D:\JavaCode\JavaSE_Code\Idea_test\libs\mysql-connector-java-5.1.37-bin.jar com.cy.mianshi.ABC
a
ab
abc
abcd
abcde
abcdef
abcdefg
abcdefgh
abcdefghi
abcdefghij
abcdefghijk
abcdefghijkl
abcdefghijklm
abcdefghijklmn
abcdefghijklmno
abcdefghijklmnop
abcdefghijklmnopq
abcdefghijklmnopqr
abcdefghijklmnopqrs
abcdefghijklmnopqrst
abcdefghijklmnopqrstu
abcdefghijklmnopqrstuv
abcdefghijklmnopqrstuvw
abcdefghijklmnopqrstuvwx
abcdefghijklmnopqrstuvwxy
abcdefghijklmnopqrstuvwxyz
b
bc
bcd
bcde
bcdef
bcdefg
bcdefgh
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bcdefghij
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bcdefghijklmnopqrst
bcdefghijklmnopqrstu
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bcdefghijklmnopqrstuvwxyz
c
cd
cde
cdef
cdefg
cdefgh
cdefghi
cdefghij
cdefghijk
cdefghijkl
cdefghijklm
cdefghijklmn
cdefghijklmno
cdefghijklmnop
cdefghijklmnopq
cdefghijklmnopqr
cdefghijklmnopqrs
cdefghijklmnopqrst
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cdefghijklmnopqrstuv
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cdefghijklmnopqrstuvwx
cdefghijklmnopqrstuvwxy
cdefghijklmnopqrstuvwxyz
d
de
def
defg
defgh
defghi
defghij
defghijk
defghijkl
defghijklm
defghijklmn
defghijklmno
defghijklmnop
defghijklmnopq
defghijklmnopqr
defghijklmnopqrs
defghijklmnopqrst
defghijklmnopqrstu
defghijklmnopqrstuv
defghijklmnopqrstuvw
defghijklmnopqrstuvwx
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e
ef
efg
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efghi
efghij
efghijk
efghijkl
efghijklm
efghijklmn
efghijklmno
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f
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fghijklmn
fghijklmno
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fghijklmnopqrs
fghijklmnopqrst
fghijklmnopqrstu
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ghijklmnopqrs
ghijklmnopqrst
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h
hi
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hijklmnopqrstuvwxy
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i
ij
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