# Problem 9

## Description

This problem was asked by Airbnb.

Given a list of integers, write a function that returns the largest sum of non-adjacent numbers. Numbers can be `0`

or negative.

For example, `[2, 4, 6, 2, 5]`

should return `13`

, since we pick `2`

, `6`

, and `5`

. `[5, 1, 1, 5]`

should return `10`

, since we pick `5`

and `5`

.

Follow-up: Can you do this in O(N) time and constant space?