KMP.java

//KMP×Ó×Ö·û´®²éÕÒ
public class KMP 
{
    private final int R;       // the radix
    private int[][] dfa;       // the KMP automoton

    private char[] pattern;    // either the character array for the pattern
    private String pat;        // or the pattern string

    /**
     * Preprocesses the pattern string.
     *
     * @param pat the pattern string
     */
    public KMP(String pat) 
    {
        this.R = 256;
        this.pat = pat;

        // build DFA from pattern
        int m = pat.length();
        dfa = new int[R][m]; 
        dfa[pat.charAt(0)][0] = 1; 
        for (int x = 0, j = 1; j < m; j++) 
        {
            for (int c = 0; c < R; c++) 
            {
                dfa[c][j] = dfa[c][x];     // Copy mismatch cases. 
            }
            dfa[pat.charAt(j)][j] = j+1;   // Set match case. 
            x = dfa[pat.charAt(j)][x];     // Update restart state. 
        } 
    } 

    /**
     * Preprocesses the pattern string.
     *
     * @param pattern the pattern string
     * @param R the alphabet size
     */
    public KMP(char[] pattern, int R) 
    {
        this.R = R;
        this.pattern = new char[pattern.length];
        for (int j = 0; j < pattern.length; j++)
        {
            this.pattern[j] = pattern[j];
        }
        
        // build DFA from pattern
        int m = pattern.length;
        dfa = new int[R][m]; 
        dfa[pattern[0]][0] = 1; 
        for (int x = 0, j = 1; j < m; j++) 
        {
            for (int c = 0; c < R; c++) 
            {
                dfa[c][j] = dfa[c][x];     // Copy mismatch cases. 
            }
            dfa[pattern[j]][j] = j+1;      // Set match case. 
            x = dfa[pattern[j]][x];        // Update restart state. 
        } 
    } 

    /**
     * Returns the index of the first occurrrence of the pattern string
     * in the text string.
     *
     * @param  txt the text string
     * @return the index of the first occurrence of the pattern string
     *         in the text string; N if no such match
     */
    public int search(String txt) 
    {
        // simulate operation of DFA on text
        int m = pat.length();
        int n = txt.length();
        int i, j;
        for (i = 0, j = 0; i < n && j < m; i++) 
        {
            j = dfa[txt.charAt(i)][j];
        }
        if (j == m) return i - m;    // found
        return n;                    // not found
    }

    /**
     * Returns the index of the first occurrrence of the pattern string
     * in the text string.
     *
     * @param  text the text string
     * @return the index of the first occurrence of the pattern string
     *         in the text string; N if no such match
     */
    public int search(char[] text) 
    {
        // simulate operation of DFA on text
        int m = pattern.length;
        int n = text.length;
        int i, j;
        for (i = 0, j = 0; i < n && j < m; i++) 
        {
            j = dfa[text[i]][j];
        }
        if (j == m) return i - m;    // found
        return n;                    // not found
    }


    /** 
     * Takes a pattern string and an input string as command-line arguments;
     * searches for the pattern string in the text string; and prints
     * the first occurrence of the pattern string in the text string.
     *
     * @param args the command-line arguments
     */
    public static void main(String[] args) 
    {
        String pat = "AACAA";
        String txt = "AABRAACADABRAACAADABRA";
        char[] pattern = pat.toCharArray();
        char[] text    = txt.toCharArray();

        KMP kmp1 = new KMP(pat);
        int offset1 = kmp1.search(txt);

        KMP kmp2 = new KMP(pattern, 256);
        int offset2 = kmp2.search(text);

        // print results
        System.out.println("text:    " + txt);

        System.out.print("pattern: ");
        for (int i = 0; i < offset1; i++)
        	System.out.print(" ");
        System.out.println(pat);

        System.out.print("pattern: ");
        for (int i = 0; i < offset2; i++)
        	System.out.print(" ");
        System.out.println(pat);
    }
}