CMU 15-112: Fundamentals of Programming and Computer Science
Extra Practice for Week 2 (Due never) Code Tracing (CT) and Reasoning Over Code (ROC) Exercises

1. Trace #1:
   
   import copy def ct1(L): a = L b = copy.copy(L) c = copy.deepcopy(L) b[1][1] = c[0][0] c[1].append(b[1][0]) a[0] = b[1] a[0][0] += b.pop()[0] return a,b,c L = [[1],[2,5]] for val in ct1(L): print(val) print(L)


2. Trace #2:
   
   def ct2(a): a[1] = "foo" a[0], a[2] = a[2], a[0] print(a) b = a b.extend([42, "wow" ]) b.pop() print(b) c = [] + b c[1:-1] = ["Hello" , "World" ] return c lst = [15, "1" , "twelve" ] print(ct2(lst)) print(lst)


3. Trace #3:
   
   import copy def ct3(L): a = L b = copy.copy(L) c = copy.deepcopy(L) b[0] = a[1] * a[1][0] a[0][0] += a.pop()[0] b[1] = c[0] return b # Be careful to get the brackets and commas right! L = [[1],[2],[3]] print(ct3(L)) print(L)


4. Trace #4:
   
   import copy def ct4(L): a = L b = copy.copy(L) c = copy.deepcopy(L) a[0] = b[1] b[1][1] = c[0] c[1].append(b[1]) a[0][0] += (b[1].pop())[0] return (a,b,c) # Be careful to get the brackets and commas right! for val in ct4([[1],[2,5]]): print(val) # prints 3 lines


5. Trace #5:
   
   import copy def ct5(a): b = a (a, c, d) = (b + [b[0]], copy.copy(b), copy.deepcopy(b)) d[1] = b[0] c[1] = d[0] b = b[0:1] + b[1:] b[0] = [3,4] a[0] += [5] c[1][0] = 1 + b[0][1] a[0][0] = 6 + d[1][0] for (s,L) in (("a",a), ("b",b), ("c",c), ("d",d)): print(s,L) a = [list(range(2-i)) for i in range(2)] print("start:", a) ct5(a) print("end:", a)

1. RC #1 of 4:
   
   def rc1(n): assert((isinstance(n, int)) and (100 <= n <= 999)) (n, r, c) = (n//100, n//10%10, n%10) L = [([0] * c) for row in range(r)] # note col is the outer loop for col in range(c): for row in range(r): L[row][col] = n n += 1 return ((L[0][2] - L[0][0] == 10) and (sum([len(R) for R in L]) == 20) and (sum(L[0]) == 42)) print(rc1(42)) # replace 42 with answer


2. RC #2 of 4:
   
   def rc2(n): assert(isinstance(n, int) and (n > 0)) (d, total) = (0, 0) while (total < 100): (d, total) = (d+1, 0) a = [d] * d b = [a] * d # note: bad way to make a 2d list for i in range(d): for j in range(d): total += b[i][j] return (n == d) print(rc2(42)) # replace 42 with answer


3. RC #3 of 4:
   
   def rc3(n): a = [[(r+c) for c in range(n)] for r in range(n)] b = [a[i][i] for i in range(n)] return (sum(b) == 20) print(rc3(42)) # replace 42 with answer


4. RC #4 of 4:
   
   def rc4(L): assert(sorted(L) == sorted(range(len(L)))) result = [] for i in range(len(L)): m = L[i] for j in range(i, len(L)): if (L[j] > m): m = L[j] result.append(m) return (result == [3, 3, 2, 1]) print(rc4(42)) # replace 42 with answer