154. 正则表达式匹配

 

154. 正则表达式匹配

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(string s, string p)

 

样例

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

思路：分多种情况递归。

class Solution {
public:
    /**
     * @param s: A string 
     * @param p: A string includes "." and "*"
     * @return: A boolean
     */
    bool isMatchCore(const string &s, int i, const string &p, int j){
        if(i==s.size() && j==p.size())return true;
        if(j==p.size())return false;
        if(i==s.size()){
            if(j+1<p.size() && p[j+1]=='*'){
                return isMatchCore(s, i, p, j+2);
            }else return false;
        }
        if(j+1<p.size() && p[j+1]=='*'){
            if(p[j]=='.'){
                return isMatchCore(s, i, p, j+2) || isMatchCore(s, i+1, p, j);
            }else{
                if(s[i]==p[j])return isMatchCore(s, i, p, j+2) || isMatchCore(s, i+1, p, j);
                else return isMatchCore(s, i, p, j+2);
            }
        }else{
            if(p[j]=='.' || s[i]==p[j])return isMatchCore(s, i+1, p, j+1);
            else return false;
        }
    }
    bool isMatch(string &s, string &p) {
        return isMatchCore(s, 0, p, 0);
    }
};