Question

containsSubSequence takes two Strings as input and returns a boolean: Returns true if the first input string contains all the characters of the second input string, in order, but not necessarily consecutively.

> HW2.containsSubSequence("abracadabra", "abcd")
true
> HW2.containsSubSequence("abracadabra", "abdc")
false

you must not use either break or continue in your code.

You are allowed to use the following methods from the Java API:

• class String
  • length
  • charAt
• class StringBuilder
  • length
  • charAt
  • append
  • toString
• class Character
  • any method

I write something but it does not work and I have no idea where is wrong. I want to check the second String's first char with the first String's every char at first. If they are the same I will set i equals the first String's length to force the program jump of the second loop(since I can't use break). Then, the second char of the second string compares with the first String's every char... when finishing all comparison. if they are the same return true otherwise false.

public static boolean containsSubSequence(String string1, String string2){
String store1 = "";
for(int j = 0; j < string2.length(); j++){
for(int i = 0; i < string1.length(); i++){
if(string2.charAt(j) == string1.charAt(i)){
store1 += string1.charAt(i);
i = string1.length();
}
}
}
if(store1.equals(string2)){
return true;
}
return false;
}

Answer 1

Program Code to Copy:

public class Subsequences {
    public static boolean containsSubSequence(String string1, String string2) {
        int i, j, flag;
        //To store indexes of first occurences of characters in string2 consecutively
        int indexes[] = new int[string2.length()];

        for (i = 0; i < string2.length(); i++) {
            flag = 0;
            for (j = 0; j < string1.length(); j++) {
                if (string1.charAt(j) == string2.charAt(i)) {
                    //Storing the index if index found
                    indexes[i] = j;
                    flag = 1;
                    j = string1.length();
                }
            }
            //Return false if element not found
            if (flag == 0)
                return false;

        }
        //Checking if indexes is strictly increasing i.e index of current character is not greater than index of next character(valid subsequence)
        for (i = 0; i < indexes.length - 1; i++) {
            if (indexes[i] > indexes[i + 1])
                return false;
        }
        //Returning true of indexes is increasing
        return true;


    }

    public static void main(String[] args) {
        System.out.println(containsSubSequence("abracadabra", "abcd"));
        System.out.println(containsSubSequence("abracadabra", "abdc"));

    }

}

Code Screenshot:

Output Screenshot: