## A Simple Interview Question

### August 14, 2018

Today’s interview question comes from Apple:

Write a program to add two integers. You may not use the

`+`

(addition) operator, but may use the`++`

(increment by 1) or`--`

(decrement by 1) operators. Be sure your solution works for both positive and negative inputs.

Your task is to write a program to add two integers. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.

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Here is my take with Julia (v. 1.0). Optimizing for number of iterations:

function add(x::Int64, y::Int64)

if x == 0

return y

elseif y == 0

return x

else

x_ = abs(x)

y_ = abs(y)

ind = argmin([x_, y_])

end

The expression (- x (- y)), equivalently x – -y for infix programmers, seems to meet the conditions of the problem.

Haskell.

Here’s a solution in C.

Examples:

function sum(a, b) {

return a – (-b);

}

Instead of the add instruction, let’s use <<, >>, &, ==, ++, and — to implement a classical binary adder. Because Python automatically promotes ints to bignums, we special case -1 to prevent infinite regress.

Another approach in Python.