CS 145 Lecture 30 – Higher Dimensions
Agenda
- what ?s
- arraylistercise
- arrays to higher dimensions
TODO
- Read sections 7.3 through 7.5 in the book. Share 2-3 questions or observations on a 1/4 sheet.
- Start homework 6. Due before November 30.
- The challenge for the second and final mercy fortnight will involve finishing homework 7 on objects before December 7. The regular due date will be before December 14. Homework 7 will be released before break and achieving it will give you the opportunity to resubmit homeworks 4, 5, and 6 before the final exam.
Note
Last time we looked at managing “growable” arrays with the ArrayList class:
1: /usr/lib/ruby/vendor_ruby/rubygems/dependency.rb:315:in `to_specs': Could not find 'coderay' (>= 0) among 94 total gem(s) (Gem::MissingSpecError) Checked in 'GEM_PATH=/var/www/.local/share/gem/ruby/3.2.0:/var/lib/gems/3.2.0:/usr/local/lib/ruby/gems/3.2.0:/usr/lib/ruby/gems/3.2.0:/usr/lib/x86_64-linux-gnu/ruby/gems/3.2.0:/usr/share/rubygems-integration/3.2.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/3.2.0:/home/johnch/.gems' , execute `gem env` for more information from /usr/lib/ruby/vendor_ruby/rubygems/dependency.rb:327:in `to_spec' from /usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_gem.rb:57:in `gem' from ./coderay:24:in `' ArrayList<Person> people = new ArrayList<Person>(); 2: Random g = new Random(); 3: people.add(g.nextPerson()); 4: people.add(g.nextPerson()); 5: people.add(g.nextPerson()); 6: people.add(g.nextPerson()); 7: people.add(g.nextPerson()); 8: System.out.println(people.size()); 9: System.out.println(people.get(1).getName()); 10: people.get(4).jump(3); 11: people.get(0).highFive(people.get(3)); 12: people.add(people.get(2)); 13: people.remove(2); 14: 15: for (int i = 1; i < people.size(); i += 2) { 16: people.get(i).sit(); 17: } 18: System.out.println(sum); 19: 20: int sum = 0; 21: for (int i = 0; i < people.size(); ++i) { 22: sum += people.get(i).getCourses(Semester.FALL, 2015).size(); 23: } 24: System.out.println(sum); 25: 26: Person winner = people.get(0); 27: for (int i = 1; i < people.size(); ++i) { 28: if (people.get(i).getDateOfBirth().isBefore(winner.getDateOfBirth())) { 29: winner = people.get(i); 30: } 31: } 32: System.out.println(winner.getName()); 33: 34: Person tmp = people.get(2); 35: people.set(2, people.get(1)); 36: people.set(1, tmp); 37: 38: for (int i = 0; i < people.size(); ++i) { 39: for (int j = 0; j < people.size(); ++j) { 40: if (i != j) { 41: people.get(i).shakeHands(people.get(j)); 42: } 43: } 44: } 45: 46: people.clear();[/precode]
Now, we missed a blackbox the other day that grows our idea of arrays into higher dimensions. Let’s have look:
To solve this we need to make arrays in higher dimensions. We saw the general pattern for making an array:
type[] id = new type[n];
The type can be anything, even another array. Suppose we want an array of int arrays? Then we substitute int[] in for type:
int[][] id = new int[outerN][innerN];
We’ll look at two-dimensional arrays through the lens of the birthday problem and generating all prefixes of an array.
Code
Prefices.java
/usr/lib/ruby/vendor_ruby/rubygems/dependency.rb:315:in `to_specs': Could not find 'coderay' (>= 0) among 94 total gem(s) (Gem::MissingSpecError) Checked in 'GEM_PATH=/var/www/.local/share/gem/ruby/3.2.0:/var/lib/gems/3.2.0:/usr/local/lib/ruby/gems/3.2.0:/usr/lib/ruby/gems/3.2.0:/usr/lib/x86_64-linux-gnu/ruby/gems/3.2.0:/usr/share/rubygems-integration/3.2.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/3.2.0:/home/johnch/.gems' , execute `gem env` for more information from /usr/lib/ruby/vendor_ruby/rubygems/dependency.rb:327:in `to_spec' from /usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_gem.rb:57:in `gem' from ./coderay:24:in `'
Bepeats.java
/usr/lib/ruby/vendor_ruby/rubygems/dependency.rb:315:in `to_specs': Could not find 'coderay' (>= 0) among 94 total gem(s) (Gem::MissingSpecError) Checked in 'GEM_PATH=/var/www/.local/share/gem/ruby/3.2.0:/var/lib/gems/3.2.0:/usr/local/lib/ruby/gems/3.2.0:/usr/lib/ruby/gems/3.2.0:/usr/lib/x86_64-linux-gnu/ruby/gems/3.2.0:/usr/share/rubygems-integration/3.2.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/3.2.0:/home/johnch/.gems' , execute `gem env` for more information from /usr/lib/ruby/vendor_ruby/rubygems/dependency.rb:327:in `to_spec' from /usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_gem.rb:57:in `gem' from ./coderay:24:in `'
Haiku
Country, state, city
Street, house number, apartment
2D is nothing
Street, house number, apartment
2D is nothing