A Google Interview question I was asked over a year ago (and didn't know the answer to). I've since learned how and here is a quick solution in JavaScript (qunit demo at http://jsfiddle.net/at4gU/). I wanted to make something Lisp-y so it takes multiple arguments, deals with negative numbers and passes JSLint (well except for the bitwise operato…

Russian.js

/*jslint bitwise: true */
var multiply = function () {
    'use strict';
    var fn = function (a, b, product) {
        if (a > 0) {
            return fn(a >> 1, b << 1, product + (a % 2 === 1 ? b : 0));
        }
        return product;
    },
        factors = Array.prototype.slice.call(arguments),
        product = factors.pop();
    while (factors.length > 0) {
        if (product < 0) {
            product = ~fn(~product + 1, factors.pop(), 0) + 1;
        } else {
            product = fn(product, factors.pop(), 0);
        }
    }
    return product;
};

//Use it like this:
alert(multiply(-3,5,-4)); //Returns 60 (-3 x 5 x -4)