题解 | #正则表达式匹配#

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) {
        int m = str.length();
        int n = pattern.length();
        vector< vector<int> > dp(m + 1, vector<int>(n + 1, 0));
        dp[0][0] = 1;
        for (int i = 0; i <= m; i++) {
            for (int j = 1; j <= n; j++) {
                if (i > 0 && str[i - 1] == pattern[j - 1]) {
                    dp[i][j] = dp[i - 1][j - 1];
                }
                else {
                    if (pattern[j-1] == '.') {
                       if(i>0) dp[i][j] = dp[i - 1][j - 1];
                    }
                    if (pattern[j-1] == '*') {
                        if(j>=2)  dp[i][j]=dp[i][j]||dp[i][j-2];
                        if(i>=1&&j>=2&&(str[i-1]==pattern[j-2]||pattern[j-2]=='.')) dp[i][j]=dp[i][j]||dp[i-1][j];
                    }
                    
                }
            }
        }
        return dp[m][n];
    }
};