JZ-052 - Regular Expression Matching

regular expression match

Topic description

Please implement a function to match regular expressions The character '.' in the pattern means any one character, and ' ' means that the character preceding it can appear any number of times (including 0).

• In this question, match means that all characters of the string match the entire pattern. For example, the string "aaa" matches the patterns "aa" and "ab ac a", but neither "aa.a" nor "ab*a".

topic link : regular expression matches

code

/**
 * 标题：正则表达式匹配
 * 题目描述
 * 请实现一个函数用来匹配包括'.'和'*'的正则表达式。模式中的字符'.'表示任意一个字符，而'*'表示它前面的字符可以出现任意次（包含0次）。
 * 在本题中，匹配是指字符串的所有字符匹配整个模式。例如，字符串"aaa"与模式"a.a"和"ab*ac*a"匹配，但是与"aa.a"和"ab*a"均不匹配
 * 题目链接：
 * https://www.nowcoder.com/practice/45327ae22b7b413ea21df13ee7d6429c?tpId=13&&tqId=11205&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking
 */
public class Jz52 {

    public boolean match(char[] str, char[] pattern) {
        int m = str.length, n = pattern.length;
        boolean[][] dp = new boolean[m + 1][n + 1];

        dp[0][0] = true;
        for (int i = 1; i <= n; i++) {
            if (pattern[i - 1] == '*') {
                dp[0][i] = dp[0][i - 2];
            }
        }

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

        return dp[m][n];
    }

    public static void main(String[] args) {
        Jz52 jz52 = new Jz52();
        System.out.println(jz52.match("aaa".toCharArray(), "a*a".toCharArray()));
    }
}

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