code: function(numbers) {
        var numbersLength = numbers.length;
        for (var i = 0; i < numbersLength; ++i) {
          var num = numbers[i];
  
          var signedNum = num << 1;
          if (num < 0) {
            signedNum = ~(signedNum);
          }
  
          numbers[i] = signedNum;
        }
  
        return this.encodeUnsignedIntegers(numbers);
      }
docs: APIMethod: encodeSignedIntegers
  Encode a list of signed integers and return an encoded string
  
  Attention: This function will modify the passed array!
  
  Parameters:
  numbers - {Array.<number>} A list of signed integers.
  
  Returns:
  {string} The encoded string.