Counting letter frequency using an array in Java

Question

I have an assignment where I have perform letter frequency analysis by iterating over the characters within a string.

I am unsure how to use an array to store the frequency of each letter. The array must be in alphabetical order and also store non-alphabetical characters (including spaces)

Unfortunately I have to use an array to store the frequency.

What would be the best way to complete this task in Java?

Do you have to support UTF or just lowercase ASCII? What do you mean by non alphabetical characters? — Karol Dowbecki, Oct 31 '19 at 23:07
@ElliottFrisch For some reason my professor has made it very clear I have to use an array. — NitroGuy, Oct 31 '19 at 23:12
The key here is to understand that a `char` is really just an `int` in desguise. — Code-Apprentice, Oct 31 '19 at 23:15
@KarolDowbecki By non alphabetical characters I mean anything that is not A - Z which may be found in text. this includes spaces, full stops, commas, question marks, numbers etc. — NitroGuy, Oct 31 '19 at 23:16
Possible duplicate of [Letter frequency array, converting int to char](https://stackoverflow.com/questions/15514440/letter-frequency-array-converting-int-to-char) — maksimov, Oct 31 '19 at 23:30

score 0 · Answer 1 · answered Nov 01 '19 at 03:12

0

Much efficient way using streams

Map<Character, Long> freq = Arrays.stream(arr).
                collect(Collectors.groupingBy(Character::charValue, Collectors.counting()));

answered Nov 01 '19 at 03:12

Shubham Gupta

11
2

LHCHIN · Accepted Answer · 2019-11-01T04:33:06.697

Ont direct way is to use 2 arrays, one for storing the character which appears in the string with case sensitive and the other one for storing its corresponding frequency.

Both arrays are declared with the size of the length of string, following sample code shows how to achieve what you want by using just array and simple logic.

Sample code

String str = "The array must be in alphabetical order and also store non-alphabetical characters (including spaces)";

char[] charArr = new char[str.length()];
int[] freqArr = new int[str.length()];
int idx = 0;
for (int i = 0; i < str.length(); i++) {
    char c = str.charAt(i);
    boolean isFound = false;
    for (idx = 0; idx < str.length(); idx++) {
        if (freqArr[idx] == 0) {
            break;
        }
        if (c == charArr[idx]) {
            freqArr[idx]++;
            isFound = true;
            break;
        }
    }
    if (!isFound) {
        charArr[idx] = c;
        freqArr[idx]++;
    }
}

//Sort charArr and freqArr arrays
char tempChar;
int tempFreq;
for (int i = 1; i < str.length(); i++) {
    for (int j = i; j > 0; j--) {
        if (charArr[j] < charArr [j - 1]) {
            tempChar = charArr[j];
            charArr[j] = charArr[j - 1];
            charArr[j - 1] = tempChar;

            tempFreq = freqArr[j];
            freqArr[j] = freqArr[j - 1];
            freqArr[j - 1] = tempFreq;
         }
    }
}

Print the letter frequency

for (int i = 0; i < str.length(); i++) {
    if (freqArr[i] != 0) {
        System.out.printf("%s:%d", charArr[i], freqArr[i]);
        System.out.println();
    }
}

Console output

[ :13],[(:1],[):1],[-:1],[T:1],[a:13],[b:3],[c:6],[d:3],[e:8],...

Counting letter frequency using an array in Java

2 Answers2