<script>

    //Javascript program for implementation of KMP pattern

    // searching algorithm

    function computeLPSArray(pat, M, lps)

    {

        // length of the previous longest prefix suffix

        var len = 0;

        var i = 1;

        lps[0] = 0; // lps[0] is always 0

        // the loop calculates lps[i] for i = 1 to M-1

        while (i < M) {

            if (pat.charAt(i) == pat.charAt(len)) {

                len++;

                lps[i] = len;

                i++;

            }

            else // (pat[i] != pat[len])

            {

                // This is tricky. Consider the example.

                // AAACAAAA and i = 7. The idea is similar

                // to search step.

                if (len != 0) {

                    len = lps[len - 1];

                    // Also, note that we do not increment

                    // i here

                }

                else // if (len == 0)

                {

                    lps[i] = len;

                    i++;

                }

            }

        }

    }

    function KMPSearch(pat,txt)

    {

        var M = pat.length;

        var N = txt.length;

        // create lps[] that will hold the longest

        // prefix suffix values for pattern

        var lps = [];

        var j = 0; // index for pat[]

        // Preprocess the pattern (calculate lps[]

        // array)

        computeLPSArray(pat, M, lps);

        var i = 0; // index for txt[]

        while (i < N) {

            if (pat.charAt(j) == txt.charAt(i)) {

                j++;

                i++;

            }

            if (j == M) {

                document.write("Found pattern " + "at index " + (i - j) + "\n");

                j = lps[j - 1];

            }

            // mismatch after j matches

            else if (i < N && pat.charAt(j) != txt.charAt(i)) {

                // Do not match lps[0..lps[j-1]] characters,

                // they will match anyway

                if (j != 0)

                    j = lps[j - 1];

                else

                    i = i + 1;

            }

        }

    }

    var txt = "ABABDABACDABABCABAB";

    var pat = "ABABCABAB";

    KMPSearch(pat, txt);

    //This code is contributed by shruti456rawal

</script>