Lost-Num.js

/*
An ordered sequence of numbers from 1 to N is given. One number might have deleted from it, then the remaining numbers were mixed. Find the number that was deleted.

Example:

The starting array sequence is [1,2,3,4,5,6,7,8,9]
The mixed array with one deleted number is [3,2,4,6,7,8,1,9]
Your function should return the int 5.
If no number was deleted from the starting array, your function should return the int 0.


*/

function findDeletedNumber(arr, mixArr) {

  let arrSum = arr.reduce((a,c) => a+c, 0)
  let mixArrSum = mixArr.reduce((a,c) => a+c, 0)
  
  return arrSum - mixArrSum
}

// two different arrays
// return the value of the missing array
// [1,2,3,4] => [4,1,2] should return 3
//find the sum of both and then subtract them!