/* Title:     Knuth-Morris-Pratt string matching algorithm
 * Author:    H.W. Lang
 *            Hochschule Flensburg, Flensburg University of Applied Sciences, Germany
 * Date:      2007
 * Mail:      lang@hs-flensburg.de
 * Web:       http://www.inf.fh-flensburg.de/lang/algorithmen/pattern/kmpen.htm
 * Reference: D.E. Knuth, J.H. Morris, V.R. Pratt: Fast Pattern Matching in Strings.
 *            SIAM Journal of Computing 6, 2, 323-350 (1977)
 */

public class KmpStringMatcher
{
    private char[] p, t;       // pattern, text
    private int m, n;          // pattern length, text length
    private String matches;    // string of match positions
    private char[] showmatches;// char array that shows matches
    private int[] b;           // used by the KMP algorithm
    private static String name="Knuth-Morris-Pratt";

    /** searches the text tt for the pattern pp
     */ 
    public void search(String tt, String pp)
    {
        setText(tt);
        setPattern(pp);
        kmpSearch();
    }

    /** sets the text
     */ 
    private void setText(String tt)
    {
        n=tt.length();
        t=tt.toCharArray();
        initmatches();
    }
    
    /** sets the pattern
     */ 
    private void setPattern(String pp)
    {
        m=pp.length();
        p=pp.toCharArray();
        b=new int[m+1];
        kmpPreprocess();
    }

    /** initializes match positions and the array showmatches
     */ 
    private void initmatches()
    {
        matches="";
        showmatches=new char[n];
        for (int i=0; i<n; i++)
            showmatches[i]=' ';
    }
    
    /** preprocessing of the pattern
     */ 
    private void kmpPreprocess()
    {
        int i=0, j=-1;
        b[i]=j;
        while (i<m)
        {
            while (j>=0 && p[i]!=p[j])
                j=b[j];
            i++;
            j++;
            b[i]=j;
        }
    }

    /** searches the text for all occurences of the pattern
     */ 
    private void kmpSearch()
    {
        int i=0, j=0;
        while (i<n)
        {
            while (j>=0 && t[i]!=p[j])
                j=b[j];
            i++;
            j++;
            if (j==m) // a match is found
            {
                report(i-m);
                j=b[j];
            }
        }
    }

    /** reports a match
     */
    private void report(int i)
    {
        matches+=i+" ";
        showmatches[i]='^';
    }

    /** returns the match positions after the search
     */ 
    public String getMatches()
    {
        return matches;
    }

    // only for test purposes
    public static void main(String[] args)
    {
        KmpStringMatcher stm=new KmpStringMatcher();
        System.out.println(name);
        String tt, pp;
        tt="abcdabcd";
        pp="abc";
        stm.search(tt, pp);
        System.out.println(pp);
        System.out.println(tt);
        System.out.println(stm.showmatches);
        System.out.println(stm.getMatches());
        tt="abababaa";
        pp="aba";
        stm.search(tt, pp);
        System.out.println(pp);
        System.out.println(tt);
        System.out.println(stm.showmatches);
        System.out.println(stm.getMatches());
    }

}    // end class KmpStringMatcher