[LeetCode][JavaScript]Regular Expression Matching

Regular Expression Matching

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

https://leetcode.com/problems/regular-expression-matching/

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第一轮遍历，把p整理成容易处理的格式，这一步不做直接处理也行。

如输入c*a*b， regMap -> ["c*", "a*", b]

然后就是花式递归，分成以下几种情况：

1. 正则数组中为单个字符，字符串的第一个必须与之匹配

2. 正则数组中包含*，枚举递归。

比如isMatch("aab", ".*b")，

当"aab"碰到".*"的时候，枚举三种情况：("aab", "b")， ("ab", ".*b")， ("b", ".*b")， ("", ".*b")

3. 当找完最后一个正则的时候，如果字符串正好用完，此时就是正确的结果，返回true。

/**
 * @param {string} s
 * @param {string} p
 * @return {boolean}
 */
var isMatch = function(s, p) {
    var regMap = [];
    buildMap(regMap, p);
    return matchReg(s, 0);
    
    function buildMap(map, reg){
        for(var i = 0; i < reg.length; i++){
            if(reg[i] === '*'){
                if(map.length >= 1){
                    map[map.length - 1] = map[map.length - 1] + "*";
                }
            }else{
                map.push(reg[i]);
            }
        }
    }
    function matchReg(str, index){
        if(index === regMap.length){
            return str === "" ? true : false;
        }

        //single char
        if(regMap[index].indexOf('*') === -1){ 
            if(str[0] === regMap[index] || (regMap[index] === "." && str != "")){
                return matchReg(str.substring(1, str.length), index + 1);
            }else{
                return false;
            }
        }

        //.*  a*
        while(str !== "" && (str[0] === regMap[index][0] || regMap[index][0] === ".")){
            if(matchReg(str, index + 1)){
                return true;
            }
            str = str.substring(1, str.length);
        }

        return matchReg(str, index + 1);
    }
};

一组Test Cases

function test(){
    console.log(isMatch("a", "ab*")); //true
    console.log(isMatch("aa", "aa")); //true
    console.log(isMatch("aa", "a*")); //true
    console.log(isMatch("aa", ".*")); //true
    console.log(isMatch("ab", ".*")); //true
    console.log(isMatch("aab", "c*a*b")); //true
    
    console.log(isMatch("aa", "a")); //false
    console.log(isMatch("aaa", "aa")); //false
    console.log(isMatch("ab", ".*c")); //false
    console.log(isMatch("a", ".*..a*")); //false
}