Return the sum of all palindromic numbers in an array

Question

I'm trying to get the sum of the palindrome numbers in an array with javascript

The code gets outputs 0 instead of getting the sum of palindrome values:

function reverse(n) {
    var rem, res = 0
    while (n > 0) {
        rem = n % 10
        res = res * 10 + rem
        n = n / 10
    }
    return res
}

function isPalindrome(n) {
    if (n == reverse(n)) return true
}

function sumArray(arr) {
    var sum = 0
    for (var i = 0; i < arr.length; i++) {
        if (arr[i] > 10 && isPalindrome(arr[i])) {
            sum += arr[i]
        }
        
    }
    console.log(sum);    
}


sumArray([12, 313, 11, 44, 9, 1])

Answer 1

The issue lies inside your reverse() function. n = n / 10 is leaving some messy decimals behind causing the loop to not terminate.

while (n > 0) {
    rem = n % 10
    res = res * 10 + rem
    n = n / 10
}

Just rounding off this result causes your code to run as expected.

while (n > 0) {
    rem = n % 10
    res = res * 10 + rem
    n = Math.round(n / 10)
}

Below is the code with that rounding change

  function reverse(n) {
    var rem, res = 0
    while (n > 0) {
      rem = n % 10
      res = res * 10 + rem
      n = Math.round(n / 10)
    }
    return res
  }

  function isPalindrome(n) {
    if (n == reverse(n)) return true
  }

  function sumArray(arr) {
    var sum = 0
    for (var i = 0; i < arr.length; i++) {
      if (arr[i] > 10 && isPalindrome(arr[i])) {
        sum += arr[i]
      }

    }
    console.log(sum);
  }

  sumArray([12, 313, 11, 44, 9, 1])