Add coding exercises for Facebook interviews

Add attempts at solving coding problems to Briefcase.

scratch/facebook/scratch.py

@@ -0,0 +1,94 @@
+# This is a scratch pad for randomly selected questions
+
+# def char_and_rest(i, xs):
+#     return xs[i], xs[:i] + xs[i+1:]
+
+# def perms(xs):
+#     if len(xs) == 1:
+#         return [xs]
+#     result = []
+#     for i in range(len(xs)):
+#         c, rest = char_and_rest(i, xs)
+#         for perm in perms(rest):
+#             result.append(c + ''.join(perm))
+#     return result
+
+# print(perms(list("woah")))
+
+# def f(take_out, dine_in, served):
+#     j, k = 0, 0
+#     for i in range(len(served)):
+#         if j < len(take_out) and served[i] == take_out[j]:
+#             j += 1
+#         elif k < len(dine_in) and served[i] == dine_in[k]:
+#             k += 1
+#         else:
+#             return False
+#     if j < len(take_out) or k < len(dine_in):
+#         return False
+#     return True
+
+# take_out = [17, 8, 24]
+# dine_in = [12, 19, 2]
+# served = [17, 8, 12, 19, 24, 2]
+# print(f(take_out, dine_in, served))
+
+# def match(a, b):
+#     if a == '{':
+#         return b == '}'
+#     if a == '[':
+#         return b == ']'
+#     if a == '(':
+#         return b == ')'
+#     return False
+
+# def f(xs):
+#     s = []
+#     for c in xs:
+#         if c in {'{', '[', '('}:
+#             s.append(c)
+#         elif c in {'}', ']', ')'}:
+#             opener = s.pop()
+#             if not match(opener, c):
+#                 return False
+#     return len(s) == 0
+
+# assert f("{[]()}")
+# assert f("{[(])}") == False
+# assert f("{[}") == False
+# print("Success!")
+
+# def valid_bst(node):
+#     lhs = max_bst_value(node.left) if node.left else float('-inf')
+#     rhs = min_bst_value(node.right) if node.right else float('inf')
+
+#     return and([
+#         lhs <= node.value,
+#         rhs > node.value,
+#         valid_bst(node.left),
+#         valid_bst(node.right),
+#     ])
+
+import random
+import math
+
+def shuffle(xs):
+    n = len(xs)
+    for i in range(n - 1):
+        j = random.randint(i + 1, n - 1)
+        xs[i], xs[j] = xs[j], xs[i]
+    return xs
+
+def as_card(i):
+    if i not in range(1, 53):
+        raise Exception("Not a card")
+    # 1
+    suit = ['Hearts', 'Clubs', 'Diamonds', 'Spades'][math.floor((i - 1) / 13)]
+    n = ['Ace',2,3,4,5,6,7,8,9,10,'Jack','Queen','King'][(i - 1) % 13]
+    return '{} of {}'.format(n, suit)
+
+xs = list(range(1, 53))
+print(xs)
+shuffle(xs)
+for x in xs:
+    print(as_card(x))