KMP prefix table

Question

I am reading about KMP for string matching.
It needs a preprocessing of the pattern by building a prefix table.
For example for the string ababaca

Answer 1

This code may not be the shortest, but easy to understand flow of code. Simple Java Code for calculating prefix-Array-

    String pattern = "ababaca";
    int i = 1, j = 0;
    int[] prefixArray = new int[pattern.length];
    while (i < pattern.length) {

        while (pattern.charAt(i) != pattern.charAt(j) && j > 0) {
            j = prefixArray[j - 1];

        }
        if (pattern.charAt(i) == pattern.charAt(j)) {
            prefixArray[i] = j + 1;
            i++;
            j++;

        } else {
            prefixArray[i] = j;
            i++;
        }
    }

    for (int k = 0; k < prefixArray.length; ++k) {
        System.out.println(prefixArray[k]);
    }

It produces the required output-

0 0 1 2 3 0 1