使用递归比较两个字符串（不区分大小写）

Question

我需要编写一个递归方法来使用字母顺序比较两个字符串而不使用 compareTo。

string1 comes before string2 returns an integer less than 0
string1 == (or indistinguishable from) string2 returns 0
string1 comes after string2 returns an integer greater than 0

我写了一个工作正常的方法，问题是如果我比较两个相似的字符串或一个字符串本身，它 returns 1 而不是 0。

知道如何优化我的方法，使其不会太长并且不会在比较两个相同的字符串时失败吗？

我认为我的部分问题是因为我将我的变量声明为静态的，但不确定我应该如何解决以在方法中声明它们。

代码：

     public class test{

            public static String s1 = "alpha";
            public static String s2 = "delta";
            public static String s3 = "omega";
            public static String s4 = "alpha";
            public static int  result;

            public static void main (String[]args){

                System.out.println(recursiveCompare(s1,s2));  // -1  good
                System.out.println(recursiveCompare(s3,s1));  //  1  good
                System.out.println(recursiveCompare(s4,s1));  //  1  FAIL!!! should be 0
                System.out.println(recursiveCompare(s2,s3));  // -1  good
                System.out.println(recursiveCompare(s1,s1));  // -1  FAIL!!! should be 0

                }

                public static int recursiveCompare(String s1, String S2){
                        if  (s1.length() ==0 || s2.length()==0){
                                if ((s1.length() ==0 && s2.length()==0)){result = 0;}
                                else if ((s1.length() !=0 || s2.length()==0)){result =  1;}
                                else if ((s1.length() ==0 || s2.length()!=0)){result = -1;}
                        }

                        else 
                        {
                            recursiveCompareHelper(s1, s2,0);
                        }
                return result;
                }

            public static int recursiveCompareHelper(String s1,String s2, int index){

                    try{

                        if (s1.regionMatches(true,index,s2,index,1)){
                                result = recursiveCompareHelper(s1,s2,(index+1));}

                            else {
                                    if (s1.charAt(index) > s2.charAt(index)){
                                        result =1;
                                    }

                                    else if (s1.charAt(index) < s2.charAt(index)){
                                        result =-1;
                                    }

                                    else if (s1.charAt(index) == s2.charAt(index)){ 
                                        result = recursiveCompareHelper(s1,s2,(index+1));
                                    }
                                }

                        } catch (StringIndexOutOfBoundsException e){
                                if      (s1.charAt(index)==0 && s2.charAt(index)== 0){result = 0;}
                                else if (s1.charAt(index)==0 && s2.charAt(index)!= 0){result = 1;}
                                else if (s1.charAt(index)!=0 && s2.charAt(index)== 0){result =-1;}
                        }

                        return result;
            }
        }

Answer 1

您不需要使用 .length() 方法。要比较字符串，您需要使用 .equals()

public static int recursiveCompare(String s1, String s2){
    if  (s1.equals(s2)) {
        return 0;
    }

    else
    {
        recursiveCompareHelper(s1, s2,0);
    }
    return result;
}

在递归 Compare(String s1, String S2) 中，您将 S2 替换为 s2。

Answer 2

首先，请注意您将 S2 作为参数传递给 recursiveCompare，而不是 s2，所以实际上你将所有内容与 "delta" 进行比较，因为 s2 是一个静态变量。其次，在比较字符串时，一旦发现差异，您就可以 return 一个答案，仅仅更改结果的值是错误的，因为它可以稍后再次更改并且 return 一个错误的答案.

这是我的解决方案，在每个递归调用中，我比较第一个字母和如果它们相等，我递归地调用该函数而没有字符串的第一个字母

public class test {

    public static String s1 = "alpha";
    public static String s2 = "delta";
    public static String s3 = "omega";
    public static String s4 = "alpha";

    public static void main(String[] args) {

        System.out.println(recursiveCompare(s1, s2));  // -1  good
        System.out.println(recursiveCompare(s3, s1));  //  1  good
        System.out.println(recursiveCompare(s4, s1));  //  1  FAIL!!! should be 0
        System.out.println(recursiveCompare(s2, s3));  // -1  good
        System.out.println(recursiveCompare(s1, s1));  // -1  FAIL!!! should be 0

    }

    public static int recursiveCompare(String s1, String s2) {
        if (s1.length() == 0 || s2.length() == 0) {
            if ((s1.length() == 0 && s2.length() == 0)) {
                return 0;
            } else if (s1.length() != 0) {
                return 1;
            } else {
                return -1;
            }
        }
        if (s1.charAt(0) < s2.charAt(0)) {
            return -1;
        } else if (s1.charAt(0) > s2.charAt(0)) {
            return 1;
        } else if (s1.charAt(0) == s2.charAt(0)) {
            return 0;
        } else {
            return recursiveCompare(s1.substring(1), s2.substring(1));
        }
    }

}

输出：

Answer 3

您在程序中犯的主要错误是在函数 recursiveCompare 中您将参数设为 S2 并且在使用变量 s2 的函数中声明为 [=14] =] 变量，因此您的函数无法给出正确的结果。请记住 java 是区分大小写的语言，在这种情况下 S2 与 s2 不同。

下面是我修改过的程序，供您理解。

    public class Test{

 /*    public static String s1 = "alpha";
        public static String s2 = "delta";
        public static String s3 = "omega";
        public static String s4 = "alpha";*/
        public static int  result;


        public static void main (String[]args){

              String s1 = "alpha";
              String s2 = "delta";
              String s3 = "omega";
              String s4 = "alpha";

             System.out.println(recursiveCompare(s1,s2));  // -1  good
             System.out.println(recursiveCompare(s3,s1));  //  1  good
            System.out.println(recursiveCompare(s4,s1));  //  1  FAIL!!! should be 0
            System.out.println(recursiveCompare(s2,s3));  // -1  good
            System.out.println(recursiveCompare(s1,s1));  // -1  FAIL!!! should be 0

            }



            public static int recursiveCompare(String s1, String S2){ 
                    if  (s1.length() ==0 || S2.length()==0){ // here you have to use S2 and not s1
                            if ((s1.length() ==0 && S2.length()==0)){result = 0;}
                            else if ((s1.length() !=0 || S2.length()==0)){result =  1;}
                            else if ((s1.length() ==0 || S2.length()!=0)){result = -1;}
                    }

                    else 
                    {
                        recursiveCompareHelper(s1, S2,0);
                    }
            return result;
            }



        public static int recursiveCompareHelper(String s1,String s2, int index){


                             // System.out.println("String are" + s1+"   "+ s2 + " index is "+ index);

                              if(index<s1.length()) {

                                 // System.out.println("Characters at  index : "+ s1.charAt(index)+ "  "+ s2.charAt(index));

                                if (s1.charAt(index) > s2.charAt(index)){
                                    //System.out.println("In the if condition");
                                    result= 1;
                                }

                                else if (s1.charAt(index) < s2.charAt(index)){
                                    //System.out.println("In the else if condition");
                                    result =-1;
                                }

                                else if (s1.charAt(index) == s2.charAt(index)){
                                    //System.out.println("Character at "+index);
                                    result = recursiveCompareHelper(s1,s2,(index+1));
                                }
                              }
                              else return 0;

                            return result;



        }
    }

使用递归比较两个字符串（不区分大小写）

Compare two String using recursion (case insensitive)

java

string

recursion

if-statement

string-comparison