Leetcode skimming ---10

subject ： Given a string  s  And a character rule  p, Implement a support '.'  and  '*'  Regular expression matching .

• '.' Match any single character
• '*' Match zero or more previous elements

Match , Is to cover   Whole string s Of , Instead of partial strings .

Input ：s = "aa", p = "a"

Output ：false

Method 1 ： Regular Expression Matching

class Solution {
public:
    bool isMatch(string s, string p) {
        int m = s.size();
        int n = p.size();
        auto matches = [&](int i, int j) {
            if (i == 0) {
                return false;
            }
            if (p[j - 1] == '.') {
                return true;
            }
            return s[i - 1] == p[j - 1];
        };
        vector<vector<int>> f(m+1, vector<int>(n + 1));
        f[0][0] = true;
        for (int i = 0; i <= m; ++i) {
            for (int j = 1; j <= n; ++j) {
                if (p[j - 1] == '*') {
                    f[i][j] |= f[i][j-2];
                    if (matches(i, j-1)) {
                        f[i][j] |= f[i-1][j];
                    }
                } else {
                    if (matches(i, j)) {
                        f[i][j] |= f[i-1][j-1];
                    }
                }
            }
        }
        return f[m][n];
    }
};

Complexity analysis

Time complexity ：O(mn)

Spatial complexity ：O(mn)