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. def ct1(s, t): result = "" for c in s: if (c.upper() not in "NO!!!"): i = t.find(c) if (result != ""): result += ":" result += "%d%s%s%s" % (i, c, s[i], t[i]) return result print(ct1("net", "two"))


2. def ct2(s): result = "" d = ord("a") for c in s.lower(): if (c.isalpha() and (ord(c) >= d)): result += str(ord(c) - d) + chr(d) d += 1 return result print(ct2("Be a CA?!?"))


3. def ct3(s): result = "" while (len(s) > 1): result += s[:1] + s[2:4] + "." s = s[1:-1:2] return result + s print(ct3("abcdefghi"))


4. def ct4(s, n): result = "" d = 0 while (n > 0) and (len(s) > 0): if (s[-1].isdigit()): result += str((n%10)%int(s[-1])) else: result += chr(ord('D')+d) n //= 10 s = s[1:-1] d += 1 return result print(ct4("abc3c3", 2468))

1. def rc1(n): assert(type(n) == int) s = str(n) return ((2000>n>1000) and (n == int(s[0]*len(s))))


2. def rc2(s, t, n): q = "" for i in range(len(s)): q += t[(i+n)%len(t)] print(q) return ((len(s) == 2*len(t)) and (not s.startswith(t)) and (q == s))


3. import string def rc3(n,k,x): s = "ab\tc\\d" assert(len(s) == n) assert(s[k] in string.whitespace) assert(s.find("b") == s.find("e") + x) return True


4. def rc4(s): assert (s[0] == "d" and len(s) == 5) for i in range(1, len(s)): if (ord(s[i]) != (i + ord(s[i-1]))): #1 + d return False return True