time complexity is O(n) where n is the max number of elements we look at to check and store in the set and O(n) space complexity because the set is proportionate to the number of elements in the array we're looking at, all of them in the worse case.

contain_duplicates.go

func containsDuplicate(nums []int) bool {
    if nums == nil {
        return false
    }
    
    set := make(map[int]bool)
    
    for _, i := range nums {
        if set[i] {
            return true
        }
        set[i] = true
    }
    
    return false
}