【剑指Offer】正则表达式匹配

题目

请实现一个函数用来匹配包含‘.’和‘’的正则表达式。模式中的字符‘.’表示任意一个字符，而‘’表示它前面的字符可以出现任意次（含0次）。在本题中，匹配是指字符串的所有字符匹配整个模式。例如，字符串“aaa”与模式“a.a”和“abaca”匹配，但与“aa.a”及“ab*a”均不匹配。

实现

public boolean match(char[] str, char[] pattern) {
    if (str == null || pattern == null)
        return false;

    return matchHelper(str, 0, pattern, 0 );
}

private boolean matchHelper(char[] str, int strIdx, char[] pattern, int patternIdx) {
    if (strIdx == str.length && patternIdx == pattern.length)
        return true;

    if (strIdx != str.length && patternIdx == pattern.length)
        return false;

    if (patternIdx + 1 < pattern.length && pattern[patternIdx+1] == '*') {
        if (strIdx < str.length && (str[strIdx] == pattern[patternIdx] || pattern[patternIdx] == '.'))
            return matchHelper(str, strIdx, pattern, patternIdx + 2)
                    || matchHelper(str , strIdx + 1, pattern, patternIdx)
                    || matchHelper(str, strIdx + 1, pattern, patternIdx + 2);
        else
            return matchHelper(str, strIdx, pattern, patternIdx + 2);
    }

    if (strIdx < str.length && (str[strIdx] == pattern[patternIdx] || pattern[patternIdx] == '.'))
        return matchHelper(str, strIdx + 1, pattern, patternIdx + 1);

    return false;
}