CMU 15-110: Principles of Computing
Week7 Practice (Due never)

Contents:

1. Code Tracing
What will this code print? Figure it out by hand, then run the code to confirm. Then slightly edit the code and try again.

Trace #1:
def ct1(L): rows = len(L) cols = len(L[0]) r = c = 0 b = L[0][0] for row in range(rows): for col in range(cols): if (L[row][col] > b): b = L[row][col] r = row c = col return [r, c] print(ct1([ [5, 2, 3, 1], [6, 0, 8, 4] ]))

Trace #2:
def make2dList(rows, cols, defaultValue=None): a=[] for row in range(rows): a.append([defaultValue]*cols) return a def print2dList(a): # For a nicer but more complex version, see http://goo.gl/eiZ42n print('[') for row in range(len(a)): print(' ', a[row]) print(']') def ct2(L): # Hint: we've seen this before, in a very different way rows = len(L) cols = len(L[0]) M = make2dList(rows+1, cols+1) for row in range(rows): total = 0 for col in range(cols): M[row][col] = L[row][col] total += M[row][col] M[row][cols] = total%2 for col in range(cols+1): total = 0 for row in range(rows): total += M[row][col] M[rows][col] = total%2 return M print2dList(ct2([ [ 0, 1, 1, 0 ], [ 1, 1, 0, 0 ], [ 1, 1, 1, 0 ], [ 0, 1, 1, 0 ] ]))

Trace #3:
def ct3(L): # Hint: we've seen this before, too! rows = len(L) cols = len(L[0]) r = c = None for row in range(rows): total = 0 for col in range(cols): total += L[row][col] if (total % 2 == 1): r = row for col in range(cols): total = 0 for row in range(rows): total += L[row][col] if (total % 2 == 1): c = col return [r, c] print(ct3([ [0, 1, 1, 0, 0], [1, 1, 0, 0, 0], [1, 1, 1, 0, 1], [0, 0, 1, 0, 0], [0, 0, 1, 0, 1] ]))