KMP字符串模式匹配学习

1.简单匹配算法：

    private int search(String source, String pattern) {
        int i = 0;
        int j = 0;

        int length = pattern.length();
        int lastIndex = source.length() - length;

        while (i <= lastIndex && j < length) {
            if (source.substring(i, i + length).equals(pattern)) {
                return i;
            } else {
                i++;
            }
        }

        return -1;
    }

 

2.KMP 算法学习

很重要的next[]获得方法：

    private void getNextVal(String pattern, int[] next) {
        // 求模式串T的next函数值并存入数组 next。

        int j = 0, k = -1;
        next[0] = -1;
        while (j < pattern.length()) {
            if (k == -1 || pattern.charAt(j) == pattern.charAt(k)) {
                ++j;
                ++k;

                if (j < pattern.length() && k < pattern.length()) {
                    if (pattern.charAt(j) != pattern.charAt(k)) {
                        next[j] = k;
                    } else {
                        next[j] = next[k];
                    }
                }

            } else {
                k = next[k];
            }
        }
    }

进行匹配：

    private int searchKMP(String source, String pattern) {
        int i = 0;
        int j = 0;

        int[] next = new int[pattern.length() + 1];
        getNextVal(pattern, next);

        while (i < source.length() && j < pattern.length()) {
            if (source.charAt(i) == pattern.charAt(j)) {
                i++;
                j++;
            } else {
                if (next[j] != -1) {
                    j = next[j];
                } else {
                    j = 0;
                    i++;
                }
            }
        }

        if (j == pattern.length()) {
            return i - j;
        } else {
            return -1;
        }
    }

 

参考：http://www.cppblog.com/oosky/archive/2006/07/06/9486.html