編寫一個遞歸方法來比較兩個字符串？

Question

可能重複：
Using Recursion To Compare Strings To Determine Which Comes First Alphabetically Java

我卡在這個遞歸問題按字母順序排序任何兩個字符串。這裏的方法簽名：

int compareTo(String s1, String s2) 

它yeilds：

returnval <0意味着s1 < s2

returnval ==0意味着s1 == s2

returnval >0意味着s1 > s2

這裏是我的代碼：

個

package bonushw; 

public class Recursion { 

    public void main (String[] args){ 
     Recursion recurse = new Recursion(); 
     System.out.println("value is: " + recurse.compareTo("bill","bill")); 
    } 

    public int compareTo (String s1, String s2) { 

    if(s1.length() == 0){ 
     return 0; 
    } 
    else if (s1.charAt(0) < s2.charAt(0)){ 
     return -1; 
    } 
    else if (s1.charAt(0) > s2.charAt(0)) { 
     return 1; 
    } 
    else { 
     return compareTo(s1.substring(1), s2.substring(1)); 
    } 
    } 

感謝

Answer 1

if(s1.length() == 0){ 
     return 0; 
    } 

這是不完整的，如果兩者都爲空，如果S2是什麼空是什麼？

Answer 2

試試這個：

class Compare 
{ 
    public static int compareTo(String s1, String s2) 
    { 
     int len = s1.length() < s2.length() ? s1.length() : s2.length(); 

     if (len == 0 && s1.length() > 0) 
      return -1; 
     else if (len == 0 && s2.length() > 0) 
      return 1; 

     for (int i = 0; i < len; ++i) 
     { 
      int v1 = s1.charAt(i); 
      int v2 = s2.charAt(i); 

      if (v1 == v2) 
       return compareTo(s1.substring(1, s1.length()), 
           s2.substring(1, s2.length())); 
      else 
       return v1 - v2; 
     } 

     return 0; 
    } 

    public static void main(String[] args) 
    { 
     System.out.println(compareTo("", ""));  // 0 
     System.out.println(compareTo("a", "a"));  // 0 
     System.out.println(compareTo("ab", "a"));  // -1 
     System.out.println(compareTo("a", "ab"));  // 1 
     System.out.println(compareTo("abc", "abc")); // 0 
    } 
}