getting indexes of different elements in the same Array

Question

I have 3 arrays example:

String[]arr1={"1150","3309","44","22","98","88","33","11","880"}
String[]arr2={"5","9","44","22","65","20","41","3","9","5"}
String[]arr3={"1","3","20","22","30","40","15","2","4","0"}

i want to get indexes for elements in the first array(arr1) that starts with ["11" , "88" , "33" ] and after getting them I have to multiply the elements of the other two arrays with the same indexes example: "1150" Starts with "11" , "3309" starts with "33" so i have to multiply 1*5 , 9*3 ..etc and store the in some variable which I can't imagine what data structure should I use for it.

 for (int k = 0; k < index - 1; k++) {
                if (arr1[k].substring(0, 2).equals("11")
                        || arr1[k].substring(0, 2).equals("88")
                        || arr1[k].substring(0, 2).equals("33"))
    {
    //don't know what should i do then
    }

    }

I tried this:

Integer x=Integer.valueOf(arr2[k])* Integer.valueOf(arr3[k]);

but then I figured out that k should have many values for the different occurrences of my targeted strings. so this line caused me an error. any help would be appreciated thanks !

Answer 1

Since it takes two to multiply, you need to make two nested loops iterating the same array arr1 . Since you do not want duplicates, start iterating the nested loop from the index one past that of the outer loop. The pattern looks like this:

for (int k = 0 ; k < arr.Length ; k++) {
    if ( /* check if k is not a good index */) {
        // If k is not an index of something we want, move on with the loop
        continue;
    }
    // Start iterating at the next position after k
    for (int m = k+1 ; m < arr.Length ; m++) {
        if (/* check if m is a good index */) {
            ... // Do something with indexes k and m
        }
    }
}

The only other thing you should do is making sure that your code does not break when arr1[i] has fewer than two characters. Currently, your code would throw an exception. A better approach is to use StartsWith("11") method, which would not throw even for an empty string.

Answer 2

Your output is unclear, still some code doing something close to what you asked :

Match.java

public enum Match {
    // Using an enum to get flexbility
    _11("11"),
    _33("33"),
    _88("88");
    public String value;
    private Match(String value) { this.value = value; }
    // This function checks if the given string starts with one of the matches
    public static Match fromString(String s) {
        for (Match m : Match.values()) { if (s.startsWith(m.value)) return m; }
        return null;
    }
}

Test.java

public class Test {

    public static void main(String[] args) {

        String[]arr1={"1150","3309","44","22","98","88","33","11","880"};
        String[]arr2={"5","9","44","22","65","20","41","3","9","5"};
        String[]arr3={"1","3","20","22","30","40","15","2","4","0"};

        Map<Match, List<Integer>> indexes = new HashMap<Match, List<Integer>>();
        // First initialize the map with empty list
        for (Match m : Match.values()) {
            indexes.put(m, new ArrayList<Integer>());
        }

        // Then a loop to find the indexes in the first array of the elements starting with one of the matches.
        for (int k = 0; k < arr1.length ; k++) {
            String cur = arr1[k];
            Match m = Match.fromString(cur);
            if (m != null) {
                indexes.get(m).add(k);
            }
        }
        // Finally loop on all patterns to get the computed result (based on 2nd and 3rd array content)
        for (Match m : Match.values()) {
            System.out.println("- " + m.name());
            for (Integer i : indexes.get(m)) {
                System.out.println("  - " + i + " > " + (Integer.valueOf(arr2[i]) * Integer.valueOf(arr3[i])));
            }
        }
    }
}

outcome:

• _11
  • 0 > 5
  • 7 > 6
• _33
  • 1 > 27
  • 6 > 615
• _88
  • 5 > 800
  • 8 > 36

Answer 3

You should store each x in an list structure, like LinkedList . You can only have one match for each value of k .

List<Integer> results = new LinkedList<>();
for(int k = 0; k < arr1.length; k++) {
    // Check if the first character is "1", "3", or "8", and that the
    // second character is the same as the first. This assumes that
    // there are no null elements and no numbers less than 10.
    if ("183".indexOf(arr1[k].charAt(0)) > 0 && arr1[k].charAt(0) == arr1[k].charAt(1)) {
        results.add(Integer.valueOf(arr2[k]) * Integer.valueOf(arr3[k]));
    }
}
// results now contains all the multiplied values.