# Leetcode 17 - Letter combinations of a phone number

`Note:`

- This is a
`backtracking`

problem. - Not like other
`combination sum`

questions. You are not just iterating a`single`

string, instead, you are iterating`many`

strings in responding to every`digit`

of digits. - Three steps to do backtracking problems
- The backtracking
`params`

are current index of digits and digits. - The
`termination condition`

is`index === digits.length`

- The logic of iterating on each level is the most important part
- Get the string according to
`index`

. - Do backtracking.

- Get the string according to

- The backtracking

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.

A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

1 | /** |