LeetCode-Regular Expression Matching

'.' 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

 

构造状态机，以正则表达式的长度作为状态，对当前所有激活的状态给予当前字符以及空字符，获取新的激活状态

class Solution {
public:
    // 0 acc and next
    // 1 acc loop or next
    // 2 not acc,quit
    // 3 not acc, go next
    int acc(int state,int input){
        if(input==-1000){
            if(state>500)return 1;
            else return 2;
        }
        if(state<500){
            if(state==input)return 0;
            else return 2;
        }
        else if(state==500)return 0;
        else if(state==1500)return 1;
        else{
            if(state-1000==input) return 1;
            else return 2;
        }

        return 0;
    }
    bool Process(vector<int>& state,vector<bool>&stateb,vector<bool>&tmpstate,int j,int val){
        int k;
        switch(val){
        case 0:
            tmpstate[j+1]=true;
            return true;
        case 1:
            tmpstate[j]=true;
            k=j+1;
            while(k<stateb.size()){
                if(state[k-1]<=500)break;
                tmpstate[k]=true;
                k++;
            }
            return true;
        default:
            return false;
        }
    }
    bool isMatch(const char *s, const char *p) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function    
        vector<int> state;
        int i=0;
        while(p[i]!='\0'){
            int st;
            if(p[i]!='.')st=(int)p[i];
            else st=500;
            i++;
            if(p[i]=='*'){st+=1000;i++;}
            state.push_back(st);
        }
        if(state.size()==0){
            if(s[0]=='\0')return true;
            else return false;
        }
        vector<bool> tmpstate;
        tmpstate.resize(state.size()+1);
        vector<bool> stateb;
        stateb.resize(state.size()+1,false);
        i=0;
        int val=acc(state[0],-1000);
        tmpstate[0]=true;
        Process(state,stateb,tmpstate,0,val);
        stateb=tmpstate;
        bool next;
        while(s[i]!='\0'){
            next=false;
            for(int j=0;j<tmpstate.size();j++)tmpstate[j]=false;
            for(int j=0;j<state.size();j++){
                if(stateb[j]){
                     val=acc(state[j],(int)s[i]);
                     bool b=Process(state,stateb,tmpstate,j,val);
                     next=next||b;
                }
            }
            stateb=tmpstate;
            if(!next)return false;
            for(int j=0;j<state.size();j++){
                if(stateb[j]){
                     val=acc(state[j],-1000);
                     Process(state,stateb,tmpstate,j,val);
                }
            }
            stateb=tmpstate;
            i++;
        }
        return stateb[state.size()];
    }
};