[LeetCode] Regular Expression Matching

class Solution {
public:
    bool isMatch(string s, string p) {
        int ans = 0;
        int n = s.size();
        int m = p.size();
        vector<vector<int>> visit(n+1, vector<int>(m+1));
        isMatch(s, p, 0, 0, visit, ans);
        return ans;
    }
    
    void isMatch(const string& s, const string& p, int u, int v, vector<vector<int>>& visit, int& ans) {
        if (visit[u][v]) return;
        visit[u][v] = 1;
        if (ans) return;
        if (u == s.size() && v == p.size()) {
            ans = 1;
            return;
        }
        
        if (p[v] == ‘*‘) {
            isMatch(s, p, u, v+1, visit, ans);
            return;
        }
        
        if (v+1 < p.size() && p[v+1] == ‘*‘) {
            // zero match
            isMatch(s, p, u, v+1, visit, ans);
        }
        
        if (u == s.size() || v == p.size()) return;
        if (p[v] == ‘.‘ || p[v] == s[u]) {
            isMatch(s, p, u+1, v+1, visit, ans);
            if (v+1 < p.size() && p[v+1] == ‘*‘) {
                isMatch(s, p, u+1, v, visit, ans);
            }
        }
    }
};