leetcode 10. Regular Expression Matching

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于 2016-03-14 11:30:20 发布

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分类专栏： leetcode 文章标签： leetcode string

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1.题目

Implement regular expression matching with support for '.' and '*'.

'.' Matches any single character.
'*' Matches zero or more of the preceding element.

The matching should cover the entire input string (not partial).

The function prototype should be:
bool isMatch(const char *s, const char *p)

Some examples:
isMatch("aa","a") → false
isMatch("aa","aa") → true
isMatch("aaa","aa") → false
isMatch("aa", "a*") → true
isMatch("aa", ".*") → true
isMatch("ab", ".*") → true
isMatch("aab", "c*a*b") → true

'.' 匹配单个的任意字符，

'*' 匹配0个或者多个前一个字符；

2.思路

利用递归。

bool isMatch(const char *s, const char *p) {
         
        if (*p == 0) return *s == 0;
        if (*(p+1) != '*')
        {
            if (*s != 0 && (*p == *s || *p == '.')) return isMatch(s+1, p+1);
            else return false;
        }
        else
        {
            // *s == *p
            while (*s != 0 && (*s == *p || *p == '.'))
            {
                if (isMatch(s, p+2)) return true;
                s++;
            }
            return (isMatch(s, p+2));
        }
    }