如何使用ArrayList打印字符串的所有子序列（）

本文概述

Java
C#
Java
C#

给定一个字符串str，任务是打印str的所有子序列。
子序列是指可以通过删除一些或不删除元素而不改变其余元素顺序的方法从另一个序列派生出来的序列。
例子：

输入：str =" abc"
输出：a b a b c ac bc abc
输入：str =" geek"
输出：g ge e ge ee gee k gk ek gek ek gek eek geek

方法:编写一个递归函数，将字符串str[0]的第一个字符追加到每个子序列的开头，然后输出从第二个字符str[1, n - 1]开始的子字符串的每个子序列。终止条件将是当传递的字符串为空时，在这种情况下，函数将返回一个空数组列表。
下面是上述方法的实现：
Java

// Java implementation of the approach import java.util.ArrayList; public class GFG { // Utility function to print the contents // of the ArrayList static void printArrayList(ArrayList< String> arrL) { arrL.remove( "" ); for ( int i = 0 ; i < arrL.size(); i++) System.out.print(arrL.get(i) + " " ); } // Function to returns the arraylist which contains // all the sub-sequences of str public static ArrayList< String> getSequence(String str) { // If string is empty if (str.length() == 0 ) { // Return an empty arraylist ArrayList< String> empty = new ArrayList< > (); empty.add( "" ); return empty; } // Take first character of str char ch = str.charAt( 0 ); // Take sub-string starting from the // second character String subStr = str.substring( 1 ); // Recurvise call for all the sub-sequences // starting from the second character ArrayList< String> subSequences = getSequence(subStr); // Add first character from str in the beginning // of every character from the sub-sequences // and then store it into the resultant arraylist ArrayList< String> res = new ArrayList< > (); for (String val : subSequences) { res.add(val); res.add(ch + val); } // Return the resultant arraylist return res; } // Driver code public static void main(String[] args) { String str = "geek" ; printArrayList(getSequence(str)); // System.out.print(getSequence(str)); } }

// C# implementation of the approach using System; using System.Collections.Generic; class GFG{ // Utility function to print the contents // of the List static void printList(List< String> arrL) { arrL.Remove( "" ); for ( int i = 0; i < arrL.Count; i++) Console.Write(arrL[i] + " " ); } // Function to returns the arraylist which contains // all the sub-sequences of str public static List< String> getSequence(String str) { // If string is empty if (str.Length == 0) { // Return an empty arraylist List< String> empty = new List< String> (); empty.Add( "" ); return empty; } // Take first character of str char ch = str[0]; // Take sub-string starting from the // second character String subStr = str.Substring(1); // Recurvise call for all the sub-sequences // starting from the second character List< String> subSequences = getSequence(subStr); // Add first character from str in the beginning // of every character from the sub-sequences // and then store it into the resultant arraylist List< String> res = new List< String> (); foreach (String val in subSequences) { res.Add(val); res.Add(ch + val); } // Return the resultant arraylist return res; } // Driver code public static void Main(String[] args) { String str = "geek" ; printList(getSequence(str)); // Console.Write(getSequence(str)); } } // This code is contributed by Rohit_ranjan

【如何使用ArrayList打印字符串的所有子序列（）】输出如下：

g e ge e ge ee gee k gk ek gek ek gek eek geek

替代解决方案：
一对一地修复字符, 并从它们开始递归地生成所有子集。
Java

// Java implementation of the approach public class sub_sequence { // Function to print all the sub-sequences // of a string public static void printSubSeq(String sub, String ans) { if (sub.length() == 0 ) { System.out.print( "" + ans + " " ); return ; } // First character of sub char ch = sub.charAt( 0 ); // Sub-string starting from second // character of sub String ros = sub.substring( 1 ); // Excluding first character printSubSeq(ros, ans); // Including first character printSubSeq(ros, ans + ch); } // Driver code public static void main(String[] args) { String str = "abc" ; printSubSeq(str, "" ); } }

// C# implementation of the approach using System; class GFG { // Function to print all the // sub-sequences of a string public static void printSubSeq( string sub, string ans) { if (sub.Length == 0) { Console.Write( "" + ans + " " ); return ; } // First character of sub char ch = sub[0]; // Sub-string starting from second // character of sub string ros = sub.Substring(1); // Excluding first character printSubSeq(ros, ans); // Including first character printSubSeq(ros, ans + ch); } // Driver code public static void Main() { string str = "abc" ; printSubSeq(str, "" ) ; } } // This code is contributed by Ryuga

输出如下：