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RegularExpressionMatching.java

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/**
* 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 RegularExpressionMatching {
public boolean isMatch(String s, String p) {
return isMatch(s, 0, p, 0);
}
private boolean isMatch(String s, int i, String p, int j) {
int ls = s.length();
int lp = p.length();
if (j == lp) {
return i == ls;
}
if ((j < lp - 1 && p.charAt(j + 1) != '*') || j == lp - 1) {
return (i < ls && s.charAt(i) == p.charAt(j) || p.charAt(j) == '.') && isMatch(s, i + 1, p, j + 1);
}
while ((i < ls && s.charAt(i) == p.charAt(j)) || (p.charAt(j) == '.' && i < ls)) {
if (isMatch(s, i, p, j + 2))
return true;
i++;
}
return isMatch(s, i, p, j + 2);
}
}
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