Minimum Sum Of Four Digit Number After Splitting Digits

Problem

You’re given a four-digit positive integer. You need to split those digits into two new numbers using every digit exactly once. Leading zeroes are allowed. Return the minimum possible sum of the two new numbers.

Approach

• 1. Take the two smallest digits and put them in the tens place of each number.Then take the two remaining digits and put them in the ones place.That minimizes the weighted contribution of the largest digits.
• 2. It's not the "cleanest" solution possible, but it was a good exercise in building and destructively slicing an array.

Edge Cases

• 4009 → zeros are allowed in the front, so result is 4 + 9 = 13
• 1111 → all digits same → 11 + 11 = 22

Reflections

With only four digits, it’s easy to spot the greedy pattern: pair the smallest digits into tens places.

In hindsight, I'd probably just use a slice of fixed length and sort it next time, much simpler and more readable.

Go Solution

func minimumSum(num int) int {
	var arr []int
	for num > 0 {
		arr = append(arr, num%10)
		num /= 10
	}

    low1, arr := minValAndMaxArr(arr)
    low2, arr := minValAndMaxArr(arr)
	return low1 * 10 + low2 * 10 + arr[0] + arr[1]
}

func minValAndMaxArr(arr []int) (int, []int) {
    min := arr[0]
    idx := 0

    for i := 1; i < len(arr); i++ {
        if arr[i] < min {
            min = arr[i]
            idx = i
        }
    }

    arr = append(arr[:idx], arr[idx+1:]...)
    return  min, arr
}

Performance

• Runtime beats: 100%
• Memory beats: 23.08%

Complexity

• Time: O(1) Constant time since input is fixed at 4 digits.
• Space: O(1) A slice of 4 ints and a few vars.