How can I encrypt a String by replacing its Chars by the Char indexes on a given String sequence?

Question

I need to create an algorithm to replace the chars of a String by the char indexes of a given sequence if the text char is available in the sequence, for example:

The sequence : 'acdfgijloprtuvx' The input : "Hello" The output must be : "He778"

'l' was replaced by 7 because it's the 7th index in the sequence.

Here's the code I started creating:

public static String encrypt(String str) {

        String sequence = "acdfgijloprtuvx";
        String result = "";

        for(int i = 0; i < str.length(); i++) {
            for(int j = 0; j < sequence.length(); j++) {
                if(str.contains(sequence)) {
                    result = str.replace(str.charAt(i), sequence.charAt(j));
                    // I don't know what to do next
                }
            }
        }
    }
}

Answer 1

Consider the following solution, it only requires a single loop and makes use of indexOf , and most importantly we correctyl use charAt to get the current letter for each loop cycle to constrect the new string using result +=... which is the same as result = result +... :

String sequence = "acdfgijloprtuvx";
String result = "";
//value to hold the current letter
String letter;

for(int i = 0; i < str.length(); i++) {
    //Get the current letter
    letter = str.charAt(i) + "";
    //If the sequence contains the letter
    if (sequence.contains(letter)){
        //Find the index of the letter and add it to the result
        result += sequence.indexOf(letter);
    }
    //Else add the original unencoded character to the result
    else{
        result += letter;
    }
}
//Print result
System.out.println("Result: " + result);

This prints the output Result: He778

The issue you were facing is that you attempted to compare the whole word with the whole sequence if(str.contains(sequence)) and you always wrote over previous data result = str.replace(str.charAt(i), sequence.charAt(j));