http://www.lintcode.com/zh-cn/problem/regular-expression-matching/

class Solution {
public:
    /**
     * @param s: A string 
     * @param p: A string includes "." and "*"
     * @return: A boolean
     */
    bool isMatch(const char *s,const char *p) {
        // write your code here
       const char*str,*ptr;
			bool start = false;
			int flag;
			int n=0,m =0 ;
			for (str = s; *str != '\0'; str++)n++;
			for (ptr = p; *ptr != '\0'; ptr++)m++;
			n--,m--;
			while (n>=0)
			{
				if (p[m] == s[n] || p[m] == '.')m--,n--;
				else if(p[m] == '*'){
					if (p[m - 1] != s[n]){//s和*前面的不一样  
							if ( p[m - 1] == '.'){//如果前面是. 
								if (m - 2 >= 0){//如果*前面至少还有2个字符
									start = true;
									flag = m; 
									while (s[n] != p[m - 2]){//如果s有存在.*前面的字符
										n--;
									}
								}
								if (m == 1) return true;//如果最后剩下.*就return true; 
							} 
					}
					else{ 
						while (p[m - 1] == s[n]){
							n--;
						}
					}
					m -= 2;
				}
				else 
					if (start){
						m = flag; 
					}
					else return false;
 
			}
			while (m>0&& p[m] == '*')
			m -= 2;
			return n==-1&&m==-1;
    }
};