LeetCode:Regular Expression Matching

Regular Expression Matching

 

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

由於只有“.”和“*”，直接想法很簡單，判定下一個是否爲“*”，如果不爲“*”則判定當前是否爲‘.’（或者任意字符），如果下一個爲“*”則需對之後從0個到最多個重複的多種情況下判定

，最後判定一下s爲空的情況。

class Solution {
public:
	bool isMatch(const char *s, const char *p) {
        if(*p == '\0')return *s == '\0';
        if(*(p+1) != '*')
        {
            return (*s == *p || (*p =='.' && *s != '\0')) && isMatch(s+1,p+1);
        }
        
        while(*s == *p || (*p == '.' && *s != '\0'))
        {
            if(isMatch(s,p+2))return true;
            s++;
        }
        return isMatch(s,p+2);
	}
};