_10.java

package com.fishercoder.solutions;

/**
 * 10. Regular Expression Matching
 *
 * Implement regular expression matching with support for '.' and '*'.
 *
 * '.' Matches any single character.
 * '*' Matches zero or more of the preceding element.
 *
 * The matching should cover the entire input string (not partial).
 *
 * The function prototype should be:
 * bool isMatch(const char *s, const char *p)
 *
 * Some examples:
 * isMatch("aa","a") → false
 * isMatch("aa","aa") → true
 * isMatch("aaa","aa") → false
 * isMatch("aa", "a*") → true
 * isMatch("aa", ".*") → true
 * isMatch("ab", ".*") → true
 * isMatch("aab", "c*a*b") → true
 */

public class _10 {

    public static class Solution1 {
        public boolean isMatch(String s, String p) {
            if (s == null || p == null) {
                return false;
            }
            boolean[][] dp = new boolean[s.length() + 1][p.length() + 1];
            dp[0][0] = true;
            for (int i = 0; i < p.length(); i++) { //here's the p's length, not s's
                if (p.charAt(i) == '*' && dp[0][i - 1]) {
                    dp[0][i + 1] = true; //here's y axis should be i+1
                }
            }
            for (int i = 0; i < s.length(); i++) {
                for (int j = 0; j < p.length(); j++) {
                    if (p.charAt(j) == '.' || p.charAt(j) == s.charAt(i)) {
                        dp[i + 1][j + 1] = dp[i][j];
                    }
                    if (p.charAt(j) == '*') {
                        if (p.charAt(j - 1) != s.charAt(i) && p.charAt(j - 1) != '.') {
                            dp[i + 1][j + 1] = dp[i + 1][j - 1];
                        } else {
                            dp[i + 1][j + 1] = (dp[i + 1][j] || dp[i][j + 1] || dp[i + 1][j - 1]);
                        }
                    }
                }
            }
            return dp[s.length()][p.length()];
        }
    }

}