A Slice of Life

Transcription

1 A Slice of Life

2 More on Slices

3 Last Time: append() and copy() Operations s := make([]int, 10)! s = append(s, 5)! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 5! 0! 1! 2! 3! 4! 5! 6! 7! 8! 9! 10! s! c := make([]int, 11)! copy(c, s)! 0! 0! 0! 0! 0! 0! 0! 0! 0! 0! 5! 0! 1! 2! 3! 4! 5! 6! 7! 8! 9! 10! c!

4 Return to Prime Numbers func ListPrimes(n int) []int {!!primebool := PrimeSieve(n)!!primes := make([]int, 0)!!for i:=range primebool {!!!if!primebool[i] && i>=2 {!!!!primes = append(primes, i)!!!}!!}!!return primes! }! This stores the primes, which we can print separately.

5 Return to Prime Numbers func PrintList(list []int) {!!for _, val := range list {!!!fmt.println(val)!!}! }! This function now works for any slice of ints.

6 Brainteasers Exercise: Given a slice a, how could you delete the element at index i?

7 Brainteasers Exercise: Given a slice a, how could you delete the element at index i? a = append(a[:i], a[i+1:])!

8 Brainteasers Exercise: Given a slice a, how could you delete the element at index i? a = append(a[:i], a[i+1:])! Exercise: Given a slice a, how would you replace the i-th element with the j-th element (thus reducing the length of the slice by 1)?

9 Brainteasers Exercise: Given a slice a, how could you delete the element at index i? a = append(a[:i], a[i+1:])! Exercise: Given a slice a, how would you replace the i-th element with the j-th element (thus reducing the length of the slice by 1)? a[i] = a[j]! a = append(a[:j], a[j+1:])!

10 The Game of Life

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12 Cellular Automata in HW3 Rule

13 Cellular Automata in HW3 Rule

14 Cellular Automata in HW3 Rule

15 Cellular Automata in HW3 Rule

16 Cellular Automata in HW3 Rule

17 Cellular Automata in HW3 Rule

18 2-D Cellular Automaton: The Game of Life 1. A live cell (dark) with < 2 live neighbors dies. 2. A live cell with 2-3 live neighbors lives on. 3. A live cell with > 3 neighbors dies. 4. A dead cell (light) with exactly three live neighbors becomes live. Neighborhood

19 2-D Cellular Automaton: The Game of Life 1. A live cell (dark) with < 2 live neighbors dies. 2. A live cell with 2-3 live neighbors lives on. 3. A live cell with > 3 neighbors dies. 4. A dead cell (light) with exactly three live neighbors becomes live.

20 Quick Quiz Exercise: What is the next iteration of this board?

21 Stable Forms

22 Quick Quiz Exercise: Carry out the next few iterations of this board. What happens?

23 Oscillators

24 Getting More Complicated

25 The Strange Behavior of the R-Pentomino

26 John Conway s Question Courtesy: Thane Plambeck! Think: Is it possible for the number of live cells to grow without bound as time goes on?

27 Bill Gosper s Glider Courtesy: Thane Plambeck!

28 Hacking the Game of Life Game of Life Problem: Input: An initial configuration of the Game of Life board, and an integer n. Output: All configurations of this board over n generations.

29 Recall: Multidimensional Arrays 4 columns var a [7][4]int! a[1][2] = 19! y := a[3][0] // gives 0! x := len(a) // gives 7! Think of as an array of length 7, where each array contains an array of length 4. 7 rows

30 Creating a 2-D Slice 2-D slices are also slices of slices we must define the outer slice first. var field [][]bool = make([][]bool, m)! m rows n columns

31 Creating a 2-D Slice 2-D slices are also slices of slices we must define the outer slice first. var field [][]bool = make([][]bool, m)! To initialize the slices in field, write an explicit loop. for row := range field {! field[row] = make([]bool, n)! }! m rows n columns

32 Creating a 2-D Slice 2-D slices are also slices of slices we must define the outer slice first. var field [][]bool = make([][]bool, m)! To initialize the slices in field, write an explicit loop. for row := range field {! field[row] = make([]bool, n)! }! Can use as 2-D array now var x = len(field)/2! var y = len(field)/2! field[x][y] = true! m rows n columns

33 Storing all n Generations Think: How do we store all n generations of a Game of Life Board (which we are storing as a 2-D slice of boolean variables)?

34 Storing all n Generations Think: How do we store all n generations of a Game of Life Board (which we are storing as a 2-D slice of boolean variables)? Answer: A 3-D slice!