Count Upside Down Numbers in a Range Using JavaScript

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