LC1. Two Sum

func twoSum(nums []int, target int) []int {
    d := map[int]int{}
 
    for i, num := range nums {
        if diffIdx, ok := d[target - num]; ok {
            return []int{diffIdx, i}
        }
 
        d[num] = i
    }
 
    return []int{}
}

Complexity

Time: $O(n)$
Space: $O(n)$