Added: isIsomorphic strings

Author: kennymkchan

README.md

@@ -276,6 +276,51 @@
   ```
   **View on Codepen:** http://codepen.io/kennymkchan/pen/xgNNNB?editors=0012
 
+  <a name="string--isIsomorphic"></a><a name="2.3"></a>
+  - **[2.3](#string--palindrome) Check if a given string is a isomorphic**
+
+    ```
+    For two strings to be isomorphic, all occurrences of a character in string A can be replaced with another character
+    to get string B. The order of the characters must be preserved. There must be one-to-one mapping for ever char of
+    string A to every char of string B.
+
+    `paper` and `title` would return true.
+    `egg` and `sad` would return false.
+    `dgg` and `add` would return true.
+    ```
+    ```javascript
+    isIsomorphic("egg", 'add'); // true
+    isIsomorphic("paper", 'title'); // true
+    isIsomorphic("kick", 'side'); // false
+
+    function isIsomorphic(firstString, secondString) {
+
+      // Check if the same lenght. If not, they cannot be isomorphic
+      if (firstString.length !== secondString.length) return false
+
+      var letterMap = {};
+
+      for (var i = 0; i < firstString.length; i++) {
+        var letterA = firstString[i],
+            letterB = secondString[i];
+
+        // If the letter does not exist, create a map and map it to the value
+        // of the second letter
+        if (letterMap[letterA] === undefined) {
+          letterMap[letterA] = letterB;
+        } else if (letterMap[letterA] !== letterB) {
+          // Eles if letterA already exists in the map, but it does not map to
+          // letterB, that means that A is mapping to more than one letter.
+          return false;
+        }
+      }
+      // If after iterating through and conditions are satisfied, return true.
+      // They are isomorphic
+      return true;
+    }
+    ```
+    **View on Codepen:** http://codepen.io/kennymkchan/pen/mRZgaj?editors=0012
+
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