KMP

/*
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 */
package array;

/**
 *
 * @author liuyuan
 */
public class KMP_practice {

    int m, n, f[];
    String str, pat;

    public KMP_practice(String str, String pat) {
        this.str = str;
        this.pat = pat;
        m = pat.length();
        n = str.length();
        f = new int[m];
    }

    public void Fail() {
        f[0] = -1;
        int i;
        for (int j = 1; j < m; j++) {
            i = f[j - 1];
            while (pat.charAt(j) != pat.charAt(i + 1) && i != -1) {
                i = f[i];
            }
            if (pat.charAt(j) == pat.charAt(i + 1)) {
                f[j] = i + 1;
            } else {
                f[j] = -1;
            }
        }
    }

    public int FastFind() {
        Fail();
        int p = 0, s = 0;
        while (p < m && s < n) {
            if (pat.charAt(p) == str.charAt(s)) {
                p++;
                s++;
            } else if (p == 0) {
                s++;
            } else {
                p = f[p - 1] + 1;
            }
        }
        if (p == m) {
            return s - m;
        } else {
            return -1;
        }
    }

    public static void main(String[] args) {
        KMP_practice test = new KMP_practice("aaaaaba", "ab");
        System.out.println(test.FastFind());
    }
}