Leetcode: Regular Expression Matching 这道每次都要看答案 心塞 啊啊啊

Problem:

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:

Code：

public class Solution {
    public boolean isMatch(String s, String p) {
        if (p.length() == 0) {
            if (s.length() == 0) return true;
            else return false;
        }
        if (p.length() == 1 || p.charAt(1) != '*') {
            if (s.length() == 0 || (s.charAt(0) != p.charAt(0) && p.charAt(0) != '.')) {
                return false;
            } else {
                return isMatch(s.substring(1), p.substring(1));
            }
        } else {
            int i = -1;
            while(i < s.length() && (i == -1 || ( (s.charAt(i) == p.charAt(0)) || p.charAt(0) == '.'))) {
                i++;
                if (isMatch(s.substring(i), p.substring(2))) return true;
            }
        }
        return false;
    }
}