44. Wildcard Matching (String; Recursion)

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

‘?‘ Matches any single character.
‘*‘ Matches any sequence of characters (including the empty sequence).不同于正则表达式中的*

*正则表达式的定义：

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

思路：当遇到*，可能匹配0, 1, 2, ...个字符=>带回溯的递归

class Solution {
public:
    bool isMatch(string s, string p) {
        star = false;
        return recursiveCheck(s,p,0,0);
    }

    bool recursiveCheck(const string &s, const string &p, int sIndex, int pIndex){
        if(sIndex >= s.length()){
            while(p[pIndex] == ‘*‘ && pIndex < p.length()) pIndex++; //s has went to end, check if the rest of p are all *
            return (pIndex==p.length());
        }

        if(pIndex >= p.length()){
            return checkStar(s,p);
        }

        switch(p[pIndex]) //p: pattern，在p中才可能出现?, *
        {
        case ‘?‘:
            return recursiveCheck(s, p, sIndex+1, pIndex+1);
            break;
        case ‘*‘: //如果当前为*， 那么可认为之前的字符都匹配上了，并且将p移动到 * 结束后的第一个字符
            star = true;  //p 每次指向的位置，要么是最开始，要么是 * 结束的第一个位置
            starIndex = pIndex;
            matchedIndex = sIndex-1;
            while(p[pIndex] == ‘*‘&& pIndex < p.length()){pIndex++;} //忽略紧接在 *后面的*
            if(pIndex==p.length()) return true;//最后一位是*
            return recursiveCheck(s,p,sIndex,pIndex); //*匹配0个字符
            break;
        default:
            if(s[sIndex] != p[pIndex]) return checkStar(s, p);
            else return recursiveCheck(s, p, sIndex+1, pIndex+1);
            break;
         }
    }

    bool checkStar(const string &s, const string &p){
        if(!star) return false;
        else {
            int pIndex = starIndex+1;
            int sIndex = ++matchedIndex; //回溯，*d多匹配一个字符
            return recursiveCheck(s, p, sIndex, pIndex);
        }
    }
private:
    int starIndex;
    int matchedIndex;
    bool star;
};