Naya Willis

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# Leetcode: Reverse Integer

Today I will be walking through the Reverse Integer Leetcode coding challenge.

# Instructions

Given a 32-bit signed integer, reverse digits of an integer.

Note:
Assume we are dealing with an environment that could only store integers within the 32-bit signed integer range: [−231, 231 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

## Overview

``````const reverseInteger = num => {
// CODE GOES HERE
}
``````

### Example 1

``````Input: x = -4253
Output: -3524
``````

### Example 2

``````Input: x = 721
Output: 127
``````

# Let's Play

Step 1

There were 2 exponent expressions that I evaluated first. 1 - (-2 ^ 31) and 2 - (2 ^ 31 - 1). I used the Math module to handle those exponent expressions.

``````let startPoint = Math.pow(-2, 31)
let endPoint = (Math.pow(-2, 31) - 1)
``````

Step 2

I converted the passed in number into a sting using the toString() method.

``````let numToString = num.toString()
``````

Step 3

Split the string, reversed it, and then joined it back together.

``````let numSplitReversedJoined = numToString.split('').reverse().join('')
``````

Step 4

Check if there is a hyphen at the beginning of the string, split the string, then use the shift method to remove and return the hyphen. Otherwise, we do nothing.

``````let hyphen = numToString.includes('-') ? numToString.split('').shift() : null
``````

Step 5

If there is a hyphen, concatenate it to the numToString then parsing it back into a number

``````let numValueWithHyphen = parseInt(hyphen + (numSplitReversedJoined))
let numValueWOHyphen = parseInt(numSplitReversedJoined)
``````

Step 6

Return either the number if it has a hyphen, or the number without it.

``````let numValue = hyphen !== null ? numValueWithHyphen : numValueWOHyphen
``````

Step 7

Lastly, check if the number reversed is within range of the startPoint and endPoint that we defined in the beginning. If it's out of range I return 0, otherwise I return the number.

``````if (numValue <= startPoint || numValue >= endPoint || numValue === 0) {
return 0
}
return xValue
``````

### All together

``````const reverseInteger = num => {
let startPoint = Math.pow(-2, 31)
let endPoint = (Math.pow(-2, 31) - 1)

let numToString = num.toString()
let numSplitReversedJoined = numToString.split('').reverse().join('')

let hyphen = numToString.includes('-') ? numToString.split('').shift() : null

let numValueWithHyphen = parseInt(hyphen + (numSplitReversedJoined))
let numValueWOHyphen = parseInt(numSplitReversedJoined)

let numValue = hyphen !== null ? numValueWithHyphen : numValueWOHyphen
if (numValue <= startPoint || numValue >= endPoint || numValue === 0) {
return 0
}
return numValue
}
``````

And, there we have it.