added regex (ignacio-chiazzo#8)

* added regex

* Update Regex.js

Author: ignacio-chiazzo

Main.js

@@ -30,4 +30,4 @@ var loadProblems = () => {
   });
 }
 
-main();
+main();

Regex.js

@@ -0,0 +1,102 @@
+/**
+URL: https://leetcode.com/problems/regular-expression-matching/description/
+ 
+Regular Expression Matching
+Given an input string (s) and a pattern (p), 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).
+
+Note:
+
+s could be empty and contains only lowercase letters a-z.
+p could be empty and contains only lowercase letters a-z, and characters like . or *.
+Example 1:
+
+Input:
+s = "aa"
+p = "a"
+Output: false
+Explanation: "a" does not match the entire string "aa".
+Example 2:
+
+Input:
+s = "aa"
+p = "a*"
+Output: true
+Explanation: '*' means zero or more of the precedeng element, 'a'. Therefore, by repeating 'a' once, it becomes "aa".
+Example 3:
+
+Input:
+s = "ab"
+p = ".*"
+Output: true
+Explanation: ".*" means "zero or more (*) of any character (.)".
+Example 4:
+
+Input:
+s = "aab"
+p = "c*a*b"
+Output: true
+Explanation: c can be repeated 0 times, a can be repeated 1 time. Therefore it matches "aab".
+Example 5:
+
+Input:
+s = "mississippi"
+p = "mis*is*p*."
+Output: false
+
+ * @param {*} s 
+ * @param {*} p 
+ */
+
+var isMatch = function(s, p) {
+  return isMatchAux(s, p, 0, 0);
+};
+
+var isMatchAux = function(str, pattern, posStr, posPat) {
+  if(posStr == str.length)
+    return posPat == pattern.length || canBeZero(pattern, posPat);
+
+  if(posPat < pattern.length - 1 && pattern.charAt(posPat + 1) == "*") {
+    const valuePattern = pattern.charAt(posPat);
+    posPat = posPat + 2;
+
+    if (isMatchAux(str, pattern, posStr, posPat)) { // 0 matches
+      return true
+    }
+    
+    while(posStr < str.length && (str.charAt(posStr) === valuePattern || valuePattern === ".")) {
+      if(isMatchAux(str, pattern, posStr + 1, posPat)) {
+        return true;
+      }
+      posStr++;
+    }
+  } else if(str.charAt(posStr) === pattern.charAt(posPat) || pattern.charAt(posPat) === ".") {
+    return isMatchAux(str, pattern, posStr + 1, posPat + 1);
+  }
+  
+  return false;
+}
+
+var canBeZero = function(pattern, posPat) {
+  while(posPat < pattern.length && pattern.charAt(posPat) == "*" || 
+    posPat < pattern.length - 1 && pattern.charAt(posPat + 1) == "*") {
+    posPat++;
+  }
+  
+  return posPat == pattern.length;
+}
+
+var main = function(){
+  console.log(isMatch("aa", "a"));
+  console.log(isMatch("aa", "a*"));
+  console.log(isMatch("a","ab*"));
+  console.log(isMatch("ab", ".*"));
+  console.log(isMatch("aab", "c*a*b"));
+  console.log(isMatch("mississippi", "mis*is*p*."));
+}
+
+main();
+module.exports.main = main;