正则表达式匹配

#include <bits/stdc++.h>

using namespace std;
//正则匹配
class Solution{
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param str string字符串
     * @param pattern string字符串
     * @return bool布尔型
     */
    bool match(string str, string pattern) {
        string s = str;
        string p = pattern;
        int n = s.size(),m = p.size();
        vector<vector<int>> dp(n+1,vector<int>(m+1,0));
        dp[0][0] = 1;
        for (int i = 1; i < m+1; ++i) {
            if(p[i-1] =='*')
            dp[0][i] = dp[0][i-2];
        }
        for (int i = 1; i < n+1 ; ++i) {
            for (int j = 1; j <m+1 ; ++j) {
                //case1,直接匹配
                if(s[i-1] == p[j-1] || p[j-1] =='.')
                    dp[i][j] = dp[i-1][j-1];
                //case2,因为*,分类讨论,
                else if(p[j-1] =='*'){
                    //匹配0次或者匹配1或者匹配2次；枚举
                    if(s[i-1] == p[j-2]  || p[j-2] == '.'){
                        dp[i][j] = dp[i][j-2] || dp[i-1][j-2] ||dp[i-1][j];
                    }
                    else if(s[i-1] != p[j-2]){
                        dp[i][j] = dp[i][j-2];
                    }
                }
            }
        }
        return dp[n][m];
    }
};