1. What will be output, how to fix, how to make thread-safe (waitGroup) 2. Remove duplicates in a slice

1. What will it output, how to fix it, how to make it thread-safe (waitGroup)

It's hard to say exactly without specific code, but a common mistake with sync.WaitGroup in Go is incorrect usage of the Add, Done, and Wait methods, which can lead to panics or deadlocks.

An example of correct usage:

var wg sync.WaitGroup
wg.Add(1)
go func() {
    defer wg.Done()
    // work
}()
wg.Wait()

It's important to call Add before starting the goroutine to avoid race conditions.

To make it thread-safe, you need to properly synchronize access to shared data, for example, using mutexes or channels.

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2. Remove duplicates from a slice

Example function to remove duplicates from a slice of strings:

func removeDuplicates(slice []string) []string {
    seen := make(map[string]struct{})
    result := []string{}
    for _, v := range slice {
        if _, ok := seen[v]; !ok {
            seen[v] = struct{}{}
            result = append(result, v)
        }
    }
    return result
}

For other types, a similar approach with a map to track unique elements can be used.