3550. Smallest Index With Digit Sum Equal to Index

You are given an integer array nums.

Return the smallest index i such that the sum of the digits of nums[i] is equal to i.

If no such index exists, return -1.

func smallestIndex(nums []int) int {
	sumDigits := func(x int) int {
		s := 0
		for x > 0 {
			s += x % 10
			x /= 10
		}
		return s
	}
	for i, v := range nums {
		if sumDigits(v) == i {
			return i
		}
	}
	return -1
}