3340. Check Balanced String

You are given a string num consisting of only digits. A string of digits is called balanced if the sum of the digits at even indices is equal to the sum of digits at odd indices.

Return true if num is balanced, otherwise return false.

package main

func isBalanced(num string) bool {
	sum := 0
	sign := 1
	for i := 0; i < len(num); i++ {
		sum += int(num[i]-'0') * sign
		sign = -sign
	}
	return sum == 0
}