minor optimize runlength

Author: Xuefeng-Zhu

src/compression/runlength/runlength.js

@@ -14,46 +14,37 @@
      * This takes O(n).
      */
     function convertToAscii(str) {
-      var result = '';
+      var result = [];
       var currentChar = '';
       var i = 0;
       for (; i < str.length; i += 1) {
         currentChar = str[i].charCodeAt(0).toString(2);
-        if (currentChar.length < 8) {
-          while (8 - currentChar.length) {
-            currentChar = '0' + currentChar;
-          }
-        }
-        result += currentChar;
+        currentChar = new Array(9 - currentChar.length).join('0') + currentChar;
+        result.push(currentChar);
       }
-      return result;
+      return result.join('');
     }
 
     /**
      * Encodes the binary string to run-length encoding.
      * Takes O(n^2).
      */
     function runLength(vector) {
-      var result = '';
+      var result = [];
       var zeros = 0;
       var zerosTemp = '';
-      var wordLength = 0;
       var i = 0;
       for (; i < vector.length; i += 1) {
         if (vector[i] === '0') {
           zeros += 1;
         } else {
           zerosTemp = zeros.toString(2);
-          wordLength = zerosTemp.length - 1;
-          while (wordLength) {
-            result = result + '1';
-            wordLength -= 1;
-          }
-          result += '0' + zerosTemp;
+          result.push(new Array(zerosTemp.length).join('1'));
+          result.push('0' + zerosTemp);
           zeros = 0;
         }
       }
-      return result;
+      return result.join('');
     }
 
     /**