使用递归反转句子的Java程序

句子是由一些定界符分隔的字符序列。此字符序列从第 0 个索引开始，最后一个索引位于 len(字符串)-1。通过反转字符串，我们交换从第 0 个索引开始的字符并将它们从末尾放置。第一个字符变成最后一个，第二个变成倒数第二个，依此类推。

例子：

Input : GeeksforGeeks
Output:    skeegrofskeeG

Input : Alice
Output: ecilA

方法：

1. 检查字符串是否为空，如果字符串为空则返回null。
2. 如果字符串为空，则返回空字符串。
3. 否则返回字符串的子字符串部分从索引 1 到字符串长度与字符串的第一个字符的连接。例如 return substring(1)+str.charAt(0);对于字符串“Mayur”返回的字符串将是“ayur”+“M”。

下面是上述方法的实现：

Java

// Java Program to Reverse a Sentence Using Recursion
import java.io.*;
  
public class GFG {
    public static String reverse_sentence(String str)
    {
        // check if str is empty
        if (str.isEmpty())
            // return the string
            return str;
        else {
            
            // extract the character at 0th index, that is
            // the character at beginning
            char ch = str.charAt(0);
            
            // append character extracted at the end
            // and pass the remaining string to the function
            return reverse_sentence(str.substring(1)) + ch;
        }
    }
  
    public static void main(String[] args)
    {
        // specify the string to reverse
        String str = "Geeksforgeeks";
        
        // call the method to reverse sentence
        String rev_str = reverse_sentence(str);
        
        // print the reversed sentence
        System.out.println(
            "Sentence in reversed form is :  " + rev_str);
  
        // creating another string with numbers
        // and special characters
        String str2 = "Alice";
        
        String rev_str2 = reverse_sentence(str2);
        
        // print the reversed sentence
        System.out.println(
            "Sentence in reversed form is :  " + rev_str2);
    }
}

输出

Sentence in reversed form is :  skeegrofskeeG
Sentence in reversed form is :  ecilA

时间复杂度： O(N)，其中 N 是字符串的长度。