给定两个字符串，确定它们是否共享一个共同的 substring

Question

This is my first Question here, I need to know why the following code does not pass Sample test case 2 in hacker rank-> Algorithms-> Strings-> Two Strings: The question is here: https://www.hackerrank.com/challenges/two-strings/problem

public static String twoStrings(String s1, String s2) {
        String answer = ""; 
        String StringToIterate = "";
        String theOtherString = "";
    
        if (s1.length() > s2.length()) {
            StringToIterate = s2;
            theOtherString  = s1;
        } else if (s1.length() < s2.length()){
            StringToIterate = s1;
            theOtherString = s2;
        } else {
            StringToIterate = s1;
            theOtherString = s2;
        }
    
    for (int i= 0; i < StringToIterate.length();i++) {
         String subS = StringToIterate.substring(i);
         if (theOtherString.contains(subS)) {
            answer = "YES";
        } else {
            answer = "NO";
       }
   }
   return answer;
   }
}

Sample test case 2:
2

aardvark

apple

beetroot

sandals

my code gives: No No but the expected output is: Yes No

Answer 1

To get this sample case working I would suggest replacing answer = "YES"; with return "YES"; .

There only has to be one substring that matches. Therefore, you should stop searching when you have found a match. Your code will happily continue searching through other substrings, even if you already found a match, and thereby setting the answer back to NO .

I don't know what the exact assignment was, but it seems that you also have to look at internal substrings. Your code only looks at the first i letters of StringToIterate .

I try to explain it using your sample case: Your code will substring check these strings

a
ap
app
appl
apple

However, p or le could've also been substrings of aardvark. Try to change your code to also check these substrings.

I hope this is enough information to keep on coding and good luck with your assignment!

Answer 2

The initial Test cases passed by doing the suggestions given (adding break; after "YES" and use substring(i,i+1)), however, when I submitted the following code, I got "Time limit exceeded" problem.

public static String twoStrings(String s1, String s2) {
        String answer = ""; 
        String StringToIterate = "";
        String theOtherString = "";

        if (s1.length() > s2.length()) {
            StringToIterate = s2;
            theOtherString  = s1;
        } else if (s1.length() < s2.length()){
            StringToIterate = s1;
            theOtherString = s2;
        } else {
            StringToIterate = s1;
            theOtherString = s2;
        }

    for (int i= 0; i < StringToIterate.length();i++) {
         String subS = StringToIterate.substring(i,i+1);
         if (theOtherString.contains(subS)) {
            answer = "YES";
            break;
        } else {
            answer = "NO";
       }
   }
   return answer;
   }
}

I cannot add return inside the for loop/if statement,because the compiler of course wants a return in the method body but outside the for loop. So, any suggestion?

Answer 3

I'm assuming one of the test cases uses a fairly large string with a lot of duplicate letters. You can try editing your solution to keep track of substrings you've already checked. For example:

public static String twoStrings(String s1, String s2) {
    String answer = ""; 
    String StringToIterate = "";
    String theOtherString = "";

    List<String> checked = new ArrayList<>();

    if (s1.length() > s2.length()) {
        StringToIterate = s2;
        theOtherString  = s1;
    } else if (s1.length() < s2.length()){
        StringToIterate = s1;
        theOtherString = s2;
    } else {
        StringToIterate = s1;
        theOtherString = s2;
    }

    for (int i= 0; i < StringToIterate.length();i++) {
        String subS = StringToIterate.substring(i,i+1);
        if (checked.contains(subS)) {
            continue;
        }

        if (theOtherString.contains(subS)) {
            answer = "YES";
            break;
        } else {
            checked.add(subS);
            answer = "NO";
        }
    }

    return answer;
}

Running your function with the checked List does not run into the time limit.

But this got me thinking "a Stream can do all of this " and that had me solving this problem in a completely different manner:

public static String twoStrings(String s1, String s2) {
    return s1.chars()
             .distinct()
             .mapToObj(c -> String.valueOf((char)c))
             .anyMatch(s2::contains) ? "YES" : "NO";
}

Without the .distinct() step I also get a timeout on tests 4 and 5, but with it all tests pass reasonably quickly.