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    fun compress(userInput: String): String {
        val charactersMap = HashMap<Char, Int>()
        val indexWithCharacter = StringBuilder()
        for (i in userInput.indices) {
            if ((i + 1) != userInput.length && userInput[i] == userInput[i + 1]) {
                if (!charactersMap.containsKey(userInput[i])) {
                    indexWithCharacter.append("$i${userInput[i]}")
                    charactersMap[userInput[i]] = i
                }
            } else { // in case character appears only one time in string

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characterAdapter.onItemClicked = { character ->
            character.let {
                if (!character.id.isNullOrBlank()) {
                    findNavController().navigate(
                        CharactersListFragmentDirections.navigateToCharacterDetailsFragment(
                            id = character.id
                        )
                    )
                }
            }

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private fun observeLiveData() {
        viewModel.character.observe(viewLifecycleOwner) { response ->
            when (response) {
                is ViewState.Loading -> {
                    binding.characterDetailsFetchProgress.visibility = View.VISIBLE
                    binding.characterDetailsNotFound.visibility = View.GONE
                }
                is ViewState.Success -> {
                    if (response.value?.data?.character == null) {
                        binding.characterDetailsFetchProgress.visibility = View.GONE

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<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/nav_main.xml"
    app:startDestination="@id/characters_list_fragment">

    <fragment
        android:id="@+id/characters_list_fragment"
        android:name="com.example.apollographqltutorial.view.ui.CharactersListFragment"

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    <fragment
        android:id="@+id/character_details_fragment"
        android:name="com.example.apollographqltutorial.view.ui.CharacterDetailsFragment"
        android:label="Character Details"
        tools:layout="@layout/fragment_character_details">

        <argument
            android:name="id"
            app:argType="string" />

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    <fragment
        android:id="@+id/characters_list_fragment"
        android:name="com.example.apollographqltutorial.view.ui.CharactersListFragment"
        android:label="List of all characters"
        tools:layout="@layout/fragment_characters_list">

        <action
            android:id="@+id/navigate_to_character_details_fragment"
            app:destination="@id/character_details_fragment" />

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<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>

        <variable
            name="query"
            type="com.example.apollographqltutorial.CharacterQuery.Data" />

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fun queryCharacter(id: String) = viewModelScope.launch {
        _character.postValue(ViewState.Loading())
        try {
            val response = repository.queryCharacter(id)
            _character.postValue(ViewState.Success(response))
        } catch (ae: ApolloException) {
            Log.d("ApolloException", "Failure", ae)
            _character.postValue(ViewState.Error("Error fetching characters"))
        }
}

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override suspend fun queryCharacter(id: String): Response<CharacterQuery.Data> {
        return webService.getApolloClient().query(CharacterQuery(id)).await()
}

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<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/nav_main.xml"
    app:startDestination="@id/characters_list_fragment">

    <fragment
        android:id="@+id/characters_list_fragment"
        android:name="com.example.apollographqltutorial.view.ui.CharactersListFragment"