leetcode: Wildcard Matching

http://oj.leetcode.com/problems/wildcard-matching/

Implement wildcard pattern matching with support for '?' and '*'.

'?' Matches any single character.
'*' Matches any sequence of characters (including the empty sequence).

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", "*") → true
isMatch("aa", "a*") → true
isMatch("ab", "?*") → true
isMatch("aab", "c*a*b") → false

思路：

参考Regular Expression Matching的思路，'*'分别尝试匹配0个或多个字符。每次遇到'*'号时，一个和n个没有区别，我们保留现场s的位置和最后一个*号位置，在需要调整的时候把已经保存的值取出来就可以了。

class Solution {
public:
    bool isMatch(const char *s, const char *p) {
        bool star = false;
        const char *saved_s = NULL, *saved_p = NULL;
        
        while (*s != '') {
            if (*p != '*') {
                if ((*s == *p) || ('?' == *p)) {
                    ++s;
                    ++p;
                }
                else {
                    if (star) {
                        s = ++saved_s;
                        p = saved_p + 1;
                    }
                    else {
                        return false;
                    }
                }
            }
            else {
                star = true;
                
                while ('*' == *p) {
                    ++p;
                }
                
                saved_s = s;
                saved_p = p - 1;
            }
        }
        
        while ('*' == *p) {
            ++p;
        }
        
        return (('' == *s) && ('' == *p));
    }
};