add AlternativeStringArrange method in string category

String/AlternativeStringArrange.js

@@ -0,0 +1,42 @@
+// Alternative arrange the two given strings in one string in O(n) time complexity.
+/**
+ * Alternative arrange the two given strings in one string in O(n) time complexity.
+ * @param {String} str1 first input string
+ * @param {String} str2 second input string
+ * @returns `String` return one alternative arrange string.
+ */
+ const AlternativeStringArrange = (str1, str2) => {
+
+    // firstly, check that both inputs are strings.
+    if (typeof str1 !== 'string' || typeof str2 !== 'string') {
+        return 'Not string(s)'
+    }
+
+    // output string vlaue.
+    let out_str = "";
+
+    // get first string length.
+    const firstStringLength = str1.length;
+    // get second string length.
+    const secondStringLength = str2.length;
+    // absolute length for oparetion.
+    let absLenght = firstStringLength > secondStringLength ? firstStringLength : secondStringLength;
+
+    // Iterate the character count until the absolute count is reached.
+    for(let charCount = 0; charCount < absLenght; charCount++){
+        // If firstStringLength is lesser than the charCount it means they are able to re-arange.
+        if(charCount < firstStringLength){
+            out_str += str1[charCount];
+        }
+
+        // If secondStringLength is lesser than the charCount it means they are able to re-arange.
+        if(charCount < secondStringLength){
+            out_str += str2[charCount];
+        }
+    }
+
+    // return the output string.
+    return out_str;
+}
+
+module.exports = AlternativeStringArrange;