Cracking the Coding Interview - Fooo

Solutions to Chapter 6 | Brain Teasers
6 1 Add arithmetic operators (plus, minus, times, divide) to make the following expression
true: 3 1 3 6 = 8 You can use any parentheses you’d like
SOLUTION
1 4 3
Cracking the Coding Interview | Concepts and Algorithms
pg 60
An interviewer is asking this problem to see how you think and approach problems—so
don’t just guess randomly
Try approaching this the following way: What sorts of operations would get us to 8? I can
think of a few:
4 * 2 = 8
16 / 2 = 8
4 + 4 = 8
Let’s start with the first one Is there any way to make 3 1 3 6 produce 4 * 2? We can easily
notice that 3 + 1 = 4 (the first two numbers) We can also notice that 6 / 3 = 2 If we had “3 1
6 3”, we’d be done, since (3 + 1)*(6 / 3) = 8 Although it seems a little unconventional to do
this, we can, in fact, just flip the 6 and the 3 to get the solution:
(( 3 + 1 ) / 3) * 6 = 8