Add solution 28.

Author: javadev

src/Algorithms/0028.implement-strstr/implement-strstr.php

@@ -0,0 +1,24 @@
+class Solution {
+
+    /**
+     * @param String $haystack
+     * @param String $needle
+     * @return Integer
+     */
+    function strStr($haystack, $needle) {
+        if(strlen($needle) == 0) return 0;
+        if(strlen($haystack) == 0) return -1;
+        if(strlen($haystack) == 1 && strlen($needle) == 1){
+            if($haystack[0] == $needle[0]){
+                return 0;
+            }
+        }
+        
+        for($i = 0; $i < strlen($haystack) - strlen($needle) + 1; $i++){
+            if($needle === substr($haystack, $i, strlen($needle))){
+                return $i;
+            }
+        }
+        return -1; 
+    }
+}