# Recognizing a Pattern in My Recursive Functions

### Robin Kim

—### November 22, 2014

Shawn Drost from Hack Reactor taught me to write recursive functions with an if-else statement:

function recursion() {if(baseCase) {// do something} else {// get me 1 step closer to the base case}}

As I was reviewing some of my curriculum material from Hack Reactor and thrashing about at codewars, I started to recognize a common pattern in my code when dealing with permutation problems that built on top of Shawn's suggestion.

Here's some code I would write if I had to find all the different permutations of a string called `problem`

.

function findAllAnswers(problem) {var partialAnswer = "";var allAnswers = [];findAnswers(problem);return allAnswers;function findAnswer(problem) {if(problem.length === 0) {allAnswers.push(partialAnswer);return;}else {// add the first bit of 'problem' to partialAnswerpartialAnswer.push(problem[0]);// explore all branches that include this first bitfindAnswer(problem.slice(1));// lets remove what we added just before the recursive callpartialAnswer = partialAnswer.substring(0, partialAnswer.length - 1);}}}

I used this approach to solve the N-Queens problem, list all possibilities of a rock-paper-scissors matchup, and find all permutations of words you could be typing into a T-9 cell phone numpad.

The key components that jump out to me are:

- I only have one
`partialAnswers`

variable that I manipulate until it meets the criteria for being a complete answer. Then I push the single solution to my`allAnswers`

array. - I explore all branches of the first possibility, then backtrack one step at a time until I return to my original state. At that point, I start exploring all branches for the next possibility.
- My code ends up being mostly simple and clean. I only need to worry about one parameter/argument in this simple problem. (My previous, unrefined approach would have required two arguments:
`remainingProblem`

and`answerSoFar`

, which can be a bit of a mess to keep in order.)

The sorcery that happens in the `else`

statement is something I may have previously struggled to come up with, but now it feels like child's play. (That's good, right?)

Next up? Maybe tail recursion.