Maps Chris Piech CS106A, Stanford University. Piech, CS106A, Stanford University

Transcription

1 Maps Chris Piech CS106A, Stanford University

2 CS106A Winter 2018 Contest

3 Why is this so fast?

4 Where are we?

5 Where are we? Karel the Robot Java Console Programs Graphics Programs Text Processing Data Structures GUIs Defining our own Variable Types

6 Collections High Level List: Array: Matrix: ArrayList<type> type[] type[][]

7 Collections High Level List: Array: Matrix: ArrayList<String> double[] int[][]

8 ArrayList index -> value

9 Arrays index -> value

10 Matrix (row, col) -> value

11 Maps can have any type for key Many examples

12 HashMap key -> value

13 Simple Example 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

14 Simple Example 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

15 Simple Example animalsoundmap Values: Keys: 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

16 Simple Example animalsoundmap Values: Keys: 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

17 Simple Example animalsoundmap Values: Keys: bark dog 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

18 Simple Example animalsoundmap Values: Keys: bark dog 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

19 Simple Example animalsoundmap Values: bark meow Keys: dog cat 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

20 Simple Example animalsoundmap Values: bark meow Keys: dog cat 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

21 Simple Example animalsoundmap Values: bark ow ow ow meow Keys: dog seal cat 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

22 Simple Example animalsoundmap Values: bark ow ow ow meow Keys: dog seal cat 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

23 Simple Example animalsoundmap Values: bark ow ow ow meow Keys: dog seal cat 1. Make a new HashMap of animal sounds 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

24 Simple Example animalsoundmap Values: bark ow ow ow meow Keys: dog seal cat 1. Make a new HashMap of animal sound 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

25 Simple Example animalsoundmap Values: bark ow ow ow meow Keys: dog seal cat 1. Make a new HashMap of animal sound 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = cat ]

26 Simple Example animalsoundmap Values: bark ow ow ow meow Keys: dog seal cat 1. Make a new HashMap of animal sound 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = cat ]

27 Simple Example animalsoundmap Values: bark ow ow ow meow Keys: dog seal cat 1. Make a new HashMap of animal sound 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = cat ]

28 My First Map HashMap<String, String> animalsoundmap = new HashMap<String, String>();

29 My First Map Key Type Value Type HashMap<String, String> animalsoundmap = new HashMap<String, String>();

30 My First Map HashMap<String, String> animalsoundmap = new HashMap<String, String>();

31 My First Map HashMap<String, String> animalsoundmap = new HashMap<String, String>();

32 My First Map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); animalsoundmap.put( dog, bark );

33 My First Map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); animalsoundmap.put( dog, bark );

34 My First Map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); animalsoundmap.put( dog, bark );

35 My First Map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); animalsoundmap.put( dog, bark );

36 My First Map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); animalsoundmap.put( dog, bark ); animalsoundmap.get( dog );

37 My First Map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); animalsoundmap.put( dog, bark ); animalsoundmap.get( dog );

38 My First Map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); animalsoundmap.put( dog, bark ); animalsoundmap.get( dog );

39 animalsoundmap My First Map Values: bark ow ow ow meow Keys: dog seal cat 1. Make a new HashMap of animal sound 2. Add elements: Put [key = dog, value = bark ] Put [key= cat, value= meow ] Put [key= seal, value= ow ow ow ] 3. Get elements: Get [key = dog ]

40 animalsoundmap My First Map Values: bark ow ow ow meow Keys: dog seal cat // 1. Make a new map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); // 2. Put things into the map animalsoundmap.put("dog", "woof"); animalsoundmap.put("cat", "meow"); animalsoundmap.put("seal", "ow ow ow"); // 3. Get things out of the map animalsoundmap.get("dog"); // "woof

41 animalsoundmap My First Map Values: bark ow ow ow meow Keys: dog seal cat // 1. Make a new map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); // 2. Put things into the map animalsoundmap.put("dog", "woof"); animalsoundmap.put("cat", "meow"); animalsoundmap.put("seal", "ow ow ow"); // 3. Get things out of the map animalsoundmap.get("dog"); // "woof" animalsoundmap.get("fox"); Piech, CS106A, Stanford // University?

42 brothers Vegard and Bård Ylvisåker Circa 2013

43 Ylvis Piech, The CS106A, Fox. Stanford Permission University asked. Pending.

44 animalsoundmap My First Map Values: bark ow ow ow meow Keys: dog seal cat // 1. Make a new map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); // 2. Put things into the map animalsoundmap.put("dog", "woof"); animalsoundmap.put("cat", "meow"); animalsoundmap.put("seal", "ow ow ow"); // 3. Get things out of the map animalsoundmap.get("dog"); // "woof" animalsoundmap.get("fox"); Piech, CS106A, Stanford // University?

45 animalsoundmap My First Map Values: bark ow ow ow meow Keys: dog seal cat // 1. Make a new map HashMap<String, String> animalsoundmap = new HashMap<String, String>(); // 2. Put things into the map animalsoundmap.put("dog", "woof"); animalsoundmap.put("cat", "meow"); animalsoundmap.put("seal", "ow ow ow"); // 3. Get things out of the map animalsoundmap.get("dog"); // "woof" animalsoundmap.get("fox"); Piech, CS106A, Stanford // University null

46 HashMaps on one slide 1. Make a HashMap HashMap<keyType, valuetype> mymap = new HashMap<keyType, valuetype>(); 2. Put and get values into a map mymap.put(key, value); mymap.get(key) // returns the corresponding value 3. Some useful other methods int size = mymap.size(); mymap.containskey(key); // returns true or false if key is in map mymap.keyset(); mymap.remove(key); // make like a tree and leave! 4. Iterate using a foreach loop for(keytype key : mymap.keyset()){ // not ordered mymap.get(key); // do something with the key/value pair }

47 Phone Book

48 Make a keyboard

49 Why is this so fast?

50 Why is this so fast? int hash(string key); * Piech, Learn CS106A, more Stanford in CS106B University