2160. Minimum Sum of Four Digit Number After Splitting Digits

How This Solution Works:

The idea of this solution is pretty simple and relies on the fact that the minimum number is made by making the biggest number the last digit and the smallest number the first. For example: If we use the digits [4, 6, 1, 3, 0, 9], the minimum number we can make is 013469.

If we want the minimum sum, we just have to add the two minimum numbers together and get the minimum sum.

So let us say that we have num = 4009. We have the digits [0, 0, 4, 9]. Then the two minimum numbers that we can make are 04, and 09.

  • For new1, the tens digit can be the smallest digit, 0.
  • For new2, the tens digit can be the second smallest digit, 0.
  • For new1, the ones digit can be the third smallest digit, 4.
  • For new2, the ones digit can be the fourth smallest digit, 9.

Walk Through the Code:

  • We can first add all the digits into the digits array.
  • Then we can sort digits.
  • The we can do new1 := digits[0] * 10 + digits[2]. This is baisically:
    • We do digits[0] * 10. This basically = Minimum number * 10. We do the * 10 because this is how we make digits[0] into the tens digit.
  • The we can do new2 := digits[1] * 10 + digits[3]. This is baisically:
    • We do digits[1] * 10. This basically = Second minimum number * 10. We do the * 10 because this is how we make digits[1] into the tens digit.
func minimumSum(num int) int {
    digits := []int{}
    
    for num > 0 {
        digits = append(digits, num % 10)
        num /= 10
    }
    
    sort.Ints(digits)
    
    new1 := digits[0] * 10 + digits[2]
    new2 := digits[1] * 10 + digits[3]
    
    return new1 + new2
}