Regular Expression Matching--LeetCode

Regular Expression Matching

(原題鏈接：點擊打開鏈接)

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

Solution：

使用遞歸算法

class Solution {
public:
    bool isMatch(string s, string p) {
        if (p.length() == 0) return s.length() == 0;
        if (p[1] == '*')
        {
            //isMatch("aab", "c*a*b") → true,返回isMatch("aab", "a*b")
            //isMatch("aa", "a*") → true，返回isMatch("a", "a*")
            //isMatch("aa", ".*") → true，返回isMatch("a", ".*")
            //isMatch("a", ".*") → true，返回isMatch("", "")
            return isMatch(s, p.substr(2)) || (s.length() != 0 && (s[0] == p[0] || p[0] == '.') && isMatch(s.substr(1), p)); 
        }
        else
        {
            if (s.length() != 0 && (s[0] == p[0] || p[0] == '.')) return isMatch(s.substr(1), p.substr(1));
            return false;
        }
    }
};