regular_expression_matching.cpp

/*
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
*/

class Solution {
public:
    bool isMatch(const char *s, const char *p) {
        if (*p == 0) return *s == 0;

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

            else
                return false;
        }
    }
};