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Minimum Spanning Trees

1. Building a Network

1-1. Minimum spanning tree (MST)

• Input: A connected, undirected graph G = (V , E) with positive edge weights.
• Output: A subset of edges E′ ⊆ E of minimum total weight such that the graph (V , E′) is connected.

Remark

The set E′ always forms a tree.

1-2. Properties of Trees

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Bidirectional Dijkstra

1. Bidirectional Search

1.1 Shortest Path

• Input: A graph G with non-negative edge weights, a source vertex s and a target vertex t.
• Output: The shortest path between s and t in G.

1.2 Why not just Dijkstra?

• O((|E| + |V |)log |V |) is pretty fast, right?
• For a graph of USA with 20M vertices and 50M edges it will work for several seconds on average
• Millions of users of Google Maps want the result in a blink of an eye, all at the same time

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Design Patterns

Week 1

1. Gang of Four's Pattern Catalogue

Design Patterns: Elements of Reusable Object-Oriented Software – Gamma, Helm, Johnson, and Vlissides

2. Categories of Patterns

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private fun getLanguage(): String {
  val lang = Locale.getDefault().language
  val country = Locale.getDefault().country
  val langTag = Locale.getDefault().toLanguageTag()
  if(lang.contains("zh")) {
    if(country == "TW") {
      return "Traditional Chinese"
    } else {
      if(langTag.contains("Hant")) {
        return "Traditional Chinese"

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<TextView
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:lineSpacingMultiplier="1.2"/>

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// Hide the keyboard.
val imm = getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager
imm.hideSoftInputFromWindow(view.windowToken, 0)

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<?xml version="1.0" encoding="utf-8"?><!--
  ~ Copyright 2018, The Android Open Source Project
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~     http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software

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Intro

Android Min and Target Versions

• The minSDK is the lowest SDK level that your app can run on. Remember that each release introduced new APIs and hardware support, so it may not make sense to make your app available to devices that don’t support your minimum feature set. Here are some examples of hardware support and features, tied to releases.
  • Home screen widgets (Cupcake)
  • Multiple finger tracking (Froyo)
  • Tablet (Honeycomb)
  • Android Beam(NFC) and BLE (Jellybean)
  • Android TV, Auto, Wear (Lollipop)
  • Pro Audio (Marshmallow)
• By comparison, the targetSDK is NOT a high pass filter -- it’s used only to declare which platform version you've tested your app on. An app targeted to a certain API or Android version will continue to be forward compatible on future releases -- the platform uses the target SDK values in case a future release makes a significant change to expected behavior, ensuring your app doesn’t break when a user’s phone gets upgraded.

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Explicit Intents launch specific activity.

Implicit Intents specify WHAT you want done and system chooses activity.

Intent Action: the type of thing that the app wants to have done on its behalf, such as ACTION_VIEW, ACTION_DIAL or ACTION_EDIT

Intent Category adds a subtype to the action, such as CATEGORY_APP_MUSIC, CATEGORY_APP_GALLERY, CATEGORY_APP_MAPS, CATEGORY_APP_CALCULATOR, CATEGORY_APP_EMAIL, CATEGORY_APP_CALENDAR

**Intent Data Type (MIME Data Type) ** allows activities to support specific data types.

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private fun ObjectAnimator.disableViewDuringAnimation(view: View) {
    addListener(object : AnimatorListenerAdapter() {
        override fun onAnimationStart(animation: Animator?) {
            view.isEnabled = false
        }

        override fun onAnimationEnd(animation: Animator?) {
            view.isEnabled = true
        }
    })