Mapping char array 2 by 2 character

Question

I have a character array like XXYYXYXYXZXZXZXYXX and I want to map it to LinkedHashMap two by two characters as shown below:

public LinkedHashMap<String, Integer> convert(char[] array) {

    LinkedHashMap<String, Integer> map = new LinkedHashMap<String, Integer>();

    int[] freq = new int[array.length];
    int i, j;

    for (i = 0; i < array.length; i+=2) {
        freq[i] = 1;
        for (j = i + 2; j < array.length; j+=2) {
            if (array[i] + array[i+1] == array[j] + array[j+1]) {
                freq[i]++;
                array[j] = '0'; //flag to check if it is already printed
                array[j+1] = '0'; //flag to check if it is already printed
            }
        }
    }

    for (i = 0; i < freq.length; i+=2) {
        if (array[i] + array[i+1] != ' ' && array[i] != '0') {                
            String dublex = ""+ array[i] + array[i+1];
            hmap.put(dublex, freq[i]);
        }
    }
    return hmap;
}

Normally it should put the following values: XX: 2 YY: 1 XY: 3 XZ: 3

But it assign the following values: XX: 2 YY: 4 XY: 3 XZ: ? not available

I am doubtful for the following lines and points:

1) I tried to use another loop value like "k" for count freq[] variable and tried to count it between 0-9 as the 18 elements are 9 two characters element: I tried to do this, but does not make sense and throws exception.

2) "0" parts added to the end of the values : I tried to add separate 0 values and check separately e.g. array[i] != '0' && array[i+1] != '0'

So, how to fix the problem?

score 1 · Accepted Answer · answered Apr 30 '20 at 23:26

1

    public static LinkedHashMap<String, Integer> convert(char[] array) {
        LinkedHashMap<String, Integer> map = new LinkedHashMap<String, Integer>();

        for (int i = 0; i < array.length - 1; i += 2) {
            map.put(array[i] + "" + array[i + 1], map.getOrDefault(array[i] + "" + array[i + 1], 0) + 1);
        }

        return map;
    }

    public static void main(String[] args) {
        System.out.println(convert("XXYYXYXYXZXZXZXYXX".toCharArray()));
    }

, output

{XX=2, YY=1, XY=3, XZ=3}

answered Apr 30 '20 at 23:26

0xh3xa

4,801
2
14
28

Unbelievable, just using half of the code lines! Thanks a lot :) – Apr 30 '20 at 23:37
1

Yes, nice answer. You could use `new String(array, i, 2)` instead of `array[i] + "" + array[i + 1]`. Also, the `for` loop condition can just be `i < array.length`, but the result is the same. – RaffleBuffle Apr 30 '20 at 23:39
@SirRaffleBuffle Could you please post it as answer? By doing this this question and answers help much more people ;) Thanks in advance. – Apr 30 '20 at 23:45
@SirRaffleBuffle I also tried your method, yes it is much more cleaner and does not change the result. If you have another suggestion I would be happy to hear. Thanks. – Apr 30 '20 at 23:48

score 0 · Answer 2 · answered May 01 '20 at 01:47

This is just a rephrasing of sc0der's answer, posted at the request of hexadecimal.

static Map<String, Integer> pairFreq(char[] array)
{
    LinkedHashMap<String, Integer> map = new LinkedHashMap<>();
    for(int i=0; i<array.length; i+=2)
    {
        String key = new String(array, i, 2);
        map.put(key, 1 + map.getOrDefault(key, 0));
    }
    return map;
}

Test:

String str = "XXYYXYXYXZXZXZXYXX";
Map<String, Integer> map = pairFreq(str.toCharArray());
for(String pair : map.keySet())
    System.out.println(pair + " : " + map.get(pair));

Output:

XX : 2
YY : 1
XY : 3
XZ : 3

Mapping char array 2 by 2 character

2 Answers2