Regular Expression Matching

Regular Expression Matching dynamic programming

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
``````

Regular Expression Matching Solution

``````public class RegularExpressionMatching {
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++) {
if(p.charAt(i) == '*' && dp[0][i - 1]) {
dp[0][i + 1] = true;
}
}

for(int i = 0; i < s.length(); i++) {
for(int j = 0; j < p.length(); j++) {
if(p.charAt(j) == '.') {
dp[i + 1][j + 1] = dp[i][j];
}

if(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()];
}
}``````