YunheWang0813
10/27/2019 - 6:56 PM

0010. Regular Expression Matching

class Solution {
public:
    bool isMatch(string s, string p) {
        int m = s.size(), n = p.size();
        vector<vector<bool>> f(m + 1, vector<bool>(n + 1, false));
        
        f[0][0] = true;
        for (int i = 1; i <= m; i++)
            f[i][0] = false;    // when p is empty, false except s is empty
        
        for (int j = 1; j <= n; j++)
            f[0][j] = j > 1 && '*' == p[j - 1] && f[0][j - 2];  // s = "", p = "a*", "a*b*", ...
        
        // Bottom-up DP table
        for (int i = 1; i <= m; i++)
            for (int j = 1; j <= n; j++)
                if (p[j - 1] != '*')
                    f[i][j] = f[i - 1][j - 1] && (s[i - 1] == p[j - 1] || '.' == p[j - 1]);
                else
                    f[i][j] = f[i][j - 2] || (s[i - 1] == p[j - 2] || '.' == p[j - 2]) && f[i - 1][j];
        
        return f[m][n];
    }
};