KMP.java

public class KMP {
    public static int[] computeLPSArray(String pattern) {
        int[] lps = new int[pattern.length()];
        int len = 0;  // Length of the previous longest prefix suffix
        int i = 1;

        while (i < pattern.length()) {
            if (pattern.charAt(i) == pattern.charAt(len)) {
                len++;
                lps[i] = len;
                i++;
            } else {
                if (len != 0) {
                    len = lps[len - 1];
                } else {
                    lps[i] = 0;
                    i++;
                }
            }
        }
        return lps;
    }

    public
 
static int KMPSearch(String pattern, String text) {
        int[] lps = computeLPSArray(pattern);
        int i = 0, j = 0;

        while (i < text.length()) {
            if (pattern.charAt(j) == text.charAt(i)) {
                j++;
                i++;
            }
            if (j == pattern.length()) {
                return i - j;  // Pattern found
            }
            if (i < text.length() && pattern.charAt(j) != text.charAt(i)) {
                if (j != 0) {
                    j = lps[j - 1];
                } else {
                    i++;
                }
            }
        }
        return -1;  // Pattern not found
    }
}