题解 | #正则表达式匹配#

import java.util.*;
public class Solution {
    public boolean match (String str, String pattern) {
        int s = str.length() + 1;
        int p = pattern.length() + 1;
        str = " " + str;
        pattern = " " + pattern;
        boolean[][] f = new boolean[s][p];
        f[0][0] = true;
        for (int i = 0; i < s; i++) {
            for (int j = 1; j < p; j++) {
                // pattern的j位置不为*
                if (pattern.charAt(j) != '*') {
                    f[i][j] = i >= 1 && f[i - 1][j - 1] && (str.charAt(i) == pattern.charAt(j) || pattern.charAt(j) == '.');
                } else {
                    //pattern的j位置为*时，可能匹配0个或多个
                    f[i][j] = (j >= 2 && f[i][j - 2]) || (i >= 1 && f[i - 1][j] && (str.charAt(i) == pattern.charAt(j - 1) || pattern.charAt(j - 1) == '.'));
                }
            }
        }
        return f[s - 1][p - 1];
    }
}