# Finding the count of total upside down numbers in a range using JavaScript

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## Upside Down Numbers

The numbers that remain the same when they’re rotated by 180 degrees are called upside down numbers.

For instance, 9116, 69.

## Problem

We are required to write a JavaScript function that takes in a range array of two numbers. Our function should return the count of all the upside down numbers that fall in the specified range.

## Example

Following is the code −

Live Demo

const range = [5, 125];
const flipNum = (number) => {
const upsideDownDigits = [0, 1, -99, -99, -99, -99, 9, -99, 8, 6];
let reverseNumArr = String(number)
.split('')
.map(val => Number(val))
.reverse();
let flipDigitsNumArr = reverseNumArr.map(val => upsideDownDigits[val]);
if (flipDigitsNumArr.includes(-99)) {
return false;
}
let flipDigitsNum = Number(
flipDigitsNumArr.reduce((accum, curr) => accum + String(curr))
);
return flipDigitsNum === number;
};
const countUpsideDown = ([lowNum, highNum]) => {
let uDNums = 0;
for (let counter = lowNum; counter <= highNum; counter++) {
uDNums += flipNum(counter) === true;
}
return uDNums;
};
console.log(countUpsideDown(range));

## Output

7
Updated on 20-Apr-2021 09:18:06