add 028 cpp version(4ms)

Author: zouwx2cs

solution/028.Implement strStr()/Solution.cpp

@@ -0,0 +1,54 @@
+class Solution {
+private:
+    vector<int> Next(string str)
+    {
+        vector<int> n(str.length()) ;
+        n[0] = -1 ; 
+        int i = 0, pre = -1 ;
+        int len = str.length() ;
+        while (i < len)
+        {
+            while (pre >= 0 && str[i] != str[pre])
+                pre = n[pre] ;
+            ++i, ++pre ;
+            if (i >= len)
+                break ;
+            if (str[i] == str[pre])
+                n[i] = n[pre] ;
+            else
+                n[i] = pre ;
+        }
+        return n ;
+    }
+public:
+    int strStr(string haystack, string needle) {
+        if (0 == needle.length())
+            return 0 ;
+        
+        vector<int> n(Next(needle)) ;
+        
+        int len = haystack.length() - needle.length() + 1 ;
+        for (int i = 0; i < len; ++i)
+        {
+            int j = 0, k = i ;
+            while (j < needle.length() && k < haystack.length())
+            {
+                if (haystack[k] != needle[j])
+                {
+                    if (n[j] >= 0)
+                    {
+                        j = n[j] ;
+                        continue ;
+                    }
+                    else
+                        break ;
+                }
+                ++k, ++j ;
+            }
+            if (j >= needle.length())
+                return k-j ;
+        }
+        
+        return -1 ;
+    }
+};