AHL: Five programming problems every Software Engineer shoul

(function (){
    function sum_for(numbers){
        var sum = 0;
        for (var i = 0; i < numbers.length; i++){
            sum += numbers[i];
        }
        return sum;
    }

    function sum_while(numbers){
        var sum = 0;
        var number;
        while (number = numbers.pop()){
            sum += number;
        }
        return sum;
    }

    function sum_recurse(total_sum, numbers){
        if (numbers.length == 0)
            return total_sum
        total_sum += numbers.pop();
        return sum_recurse(total_sum, numbers);
    }

    console.log(sum_for([1, 2, 4, 8, 16]));
    console.log(sum_while([1, 2, 4, 8, 16]));
    console.log(sum_recurse(0, [1, 2, 4, 8, 16]));

    function combine_lists(list_a, list_b){
        var combined_array = [];
        for (var i = 0; i < (list_a.length + list_b.length) / 2; i++)
        {
            var a = list_a[i];
            var b = list_b[i];

            if (a)
               combined_array.push(list_a[i]);

            if (b)
               combined_array.push(list_b[i]);
        }
        return combined_array;
    }

    console.log(combine_lists(["a", "b", "c"], [1, 2, 3]));

    function generate_fibonacci(fib_nums){
        var num_c = fib_nums[fib_nums.length - 2] + fib_nums[fib_nums.length - 1];
        fib_nums.push(num_c);
        if (fib_nums.length === 100)
            return fib_nums
        else
            return generate_fibonacci(fib_nums)
    }

    console.log(generate_fibonacci([0, 1]));

    function make_big_number(set){
        var max_length = 0;

        for (var i = 0; i < set.length; i++){
            var set_s = (set[i] + "");
            if (set_s.length > max_length)
                max_length = set_s.length;
        }

        var padded_set = [];

        for (var i = 0; i < set.length; i++){
            var working_num = set[i] + "";
            if (working_num.length < max_length){
                for (var j = 0; j < max_length - working_num.length; j++){
                    working_num = working_num + 0;
                }
            }
            padded_set.push(working_num );
        }

        var sort_padded = padded_set.slice(0).sort().reverse();
        var return_arr = [];
        for (var i = 0; i < sort_padded.length; i++){
            return_arr[i] = set[padded_set.indexOf(sort_padded[i])];
        }

        return return_arr.join("");

    }

    console.log(make_big_number([50, 2, 1, 9]));



    function find_all_combinations(number_string, valid_characters){
        var recurse = function(){
            return function(working_string, level, set){
                level += 1;
                for (var i = 0; i < valid_characters.length; i++)
                {
                    var op_string = working_string + valid_characters[i];

                    if (op_string.length === number_string.length - 1){
                        var merged_string = "";
                        for (var j = 0; j < number_string.length; j++){
                            merged_string += number_string[j];
                            if (typeof op_string[j] !== 'undefined')
                               merged_string += op_string[j];
                        }
                        var math_string = merged_string.replace(/\s+/g, '');
                        if (+eval(math_string) === 100)
                           set.push(math_string);
                    }

                    if (level < number_string.length - 1)
                    {
                        recurse(op_string, level, set);
                    }
                }
                return set;
            }
        }();

        return recurse("", 0, []);
    }

    console.log(find_all_combinations("123456789", " -+"));

})();