<gh_stars>0using System.Collections.Generic;

namespace GsvGameMaps;

public class KMPSearch
{
    static List<int> Search(string pat, string txt)
    {
        List<int> result = new List<int>();
        int M = pat.Length;
        int N = txt.Length;

        // create lps[] that will hold the longest
        // prefix suffix values for pattern
        int[] lps = new int[M];
        int j = 0; // index for pat[]

        // Preprocess the pattern (calculate lps[]
        // array)
        computeLPSArray(pat, M, lps);

        int i = 0; // index for txt[]
        while (i < N) {
            if (pat[j] == txt[i]) {
                j++;
                i++;
            }
            if (j == M) {
                result.Add(i - j);
                j = lps[j - 1];
            }

            // mismatch after j matches
            else if (i < N && pat[j] != txt[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;
            }
        }

        return result;
    }

    static void computeLPSArray(string pat, int M, int[] lps)
    {
        // length of the previous longest prefix suffix
        int len = 0;
        int 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[i] == pat[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++;
                }
            }
        }
    }

    // Driver program to test above function
    public static List<int> KMPSearchMain(string txt, string pattern)
    {
        var result = Search(pattern, txt);
        return result;
    }
}
