kmp算法的java实现

kmp算法，java代码。先看代码，有空再来细说。

public class TestString {

    private String testStr = "ACHHEEDHEYBGREATEBALLHEYUSHIGEDAHAORENALORENZOYESHIHAORENHEYU";

    // 朴素的匹配算法
    public int bf(String s) {
        int i = 0;
        int j = 0;

        while (i < testStr.length() && j < s.length()) {
            if (testStr.charAt(i) == s.charAt(j)) {
                i++;
                j++;
            } else {
                i = i - j + 1;
                j = 0;
            }
        }
        if (j == s.length()) {
            return i - j;
        } else {
            return -1;
        }
    }

    // KMP算法
    public int kmp(String s) {
        int i = 0;
        int j = 0;
        int[] next = new int[s.length()];
        next = preNext(s);
        while (i < testStr.length() && j < s.length()) {
            if (j == -1 || testStr.charAt(i) == s.charAt(j)) {
                i++;
                j++;
            } else {
                j = next[j];
            }
        }
        if (j == s.length()) {
            return i - j;
        } else {
            return -1;
        }
    }

    // 前缀函数
    public int[] preNext(String s) {
        int[] next = new int[s.length()];
        int i, j, temp;
        for (i = 0; i < s.length(); i++) {
            if (i == 0) {
                next[i] = -1;
            } else if (i == 1) {
                next[i] = 0;
            } else {
                temp = i - 1;
                for (j = temp; j > 0; j--) {
                    if (s.charAt(i) == s.charAt(j)) {
                        next[i] = j;
                        break;
                    }
                }
                if (j == 0)
                    next[i] = 0;
            }
        }
        return next;
    }

    public static void main(String[] args) {
        TestString ts = new TestString();
        System.out.println(" bf: " + ts.bf("HEYU"));
        System.out.println("kmp: " + ts.kmp("HEYU"));
    }

}