Understanding Knuth-Morris-Pratt Algorithm

Question

Can someone explain this to me? I\'ve been reading about it and it still is hard to follow.

text : ababdbaababa
pattern: ababa

table for ababa is -1 0 0

Answer 1

A Complete Solution using Java:

package src.com.recursion;
/*
 * This Expains the Search of pattern in text in O(n)
 */
public class FindPatternInText {
    public int checkIfExists(char[] text, char[] pattern) {
        int index = 0;
        int[] lps = new int[pattern.length];
        createPrefixSuffixArray(pattern, lps);
        int i = 0;
        int j = 0;
        int textLength = text.length;
        while (i < textLength) {
            if (pattern[j] == text[i]) {
                j++;
                i++;
            }
            if (j == pattern.length)
                return i - j;
            else if (i < textLength && pattern[j] != text[i]) {
                if (j != 0) {
                    j = lps[j - 1];
                } else {
                    i++;
                }
            }
        }
        return index;
    }

    private void createPrefixSuffixArray(char[] pattern, int[] lps) {
        lps[0] = 0;
        int index = 0;
        int i = 1;
        while (i < pattern.length) {
            if (pattern[i] == pattern[index]) {
                lps[i] = index;
                i++;
                index++;
            } else {
                if (index != 0) {
                    index = lps[index - 1];
                } else {
                    lps[i] = 0;
                    i++;
                }
            }
        }
    }
    public static void main(String args[]) {
        String text = "ABABDABACDABABCABAB";
        String pattern = "ABABCABAB";
        System.out.println("Point where the pattern match starts is "
                + new FindPatternInText().checkIfExists(text.toCharArray(), pattern.toCharArray()));
    }
}