Add 'Regular Expression Matching' solution.

Author: liuyingshan

Find_Minimum_in_Rotated_Sorted_Array_II.cpp

@@ -32,4 +32,4 @@ class Solution {
     int findMin(vector<int> &num) {
         return findSubMin(num, 0, num.size()-1);
     }
-};
+};

Regular_Expression_Matching.cpp

@@ -0,0 +1,44 @@
+/*
+  '.' 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") ¡ú false
+    isMatch("aa","aa") ¡ú true
+    isMatch("aaa","aa") ¡ú false
+    isMatch("aa", "a*") ¡ú true
+    isMatch("aa", ".*") ¡ú true
+    isMatch("ab", ".*") ¡ú true
+    isMatch("aab", "c*a*b") ¡ú true
+*/
+
+class Solution {
+public:
+    bool isEqual(char s, char p) {
+        if (s == p || p == '.' && s != '\0') return true;
+        return false;
+    }
+    
+    bool isMatch(const char *s, const char *p) {
+        if (*s == '\0' && *p == '\0') return true;
+        
+        if (*p != '\0' && *(p + 1) == '*') {
+            // '*' represents zero of preceding element.
+            if (isMatch(s, p + 2)) return true;
+            // '*' represents one or more of preceding element.
+            while (isEqual(*s, *p)) {
+                ++s;
+                if (isMatch(s, p + 2)) return true;
+            }
+        } else if (isEqual(*s, *p)) {
+            if (isMatch(s + 1, p + 1)) return true;
+        }
+        
+        return false;
+    }
+};