ArrayList matachedAtindex;

    void KMPSearch(char[] pat, char[] txt) {
        int m = pat.length;
        int n = txt.length;
        int j = 0;
        int i = 0;
        matachedAtindex = new ArrayList<>();
        lpsCompute(pat);
        while (i < n) {
            if (pat[j] == txt[i]) {
                j++;
                i++;
            }
            if (j == m) {
                matachedAtindex.add((i - j));
                j = lps[j - 1];
            } else if (i < n && pat[j] != txt[i]) {
                if (j != 0)
                    j = lps[j - 1];
                else
                    i = i + 1;
            }
        }
    }
    
    static int lps[];

    static void lpsCompute(char[] pat) {
        int n = pat.length;
        lps = new int[n];
        int j = 0;
        int i = 1;
        while (i < n) {
            if (pat[i] == pat[j]) {
                j++;
                lps[i] = j;
                i++;
            } else {
                if (j != 0) {
                    j = lps[j - 1];
                } else {
                    lps[i] = j;
                    i++;
                }
            }
        }
    }