if current.value == k:
equal.next_node = current
equal = equal.next_node
elif current.value > k:
more.next_node = current
more = more.next_node
else:
less.next_node = current
less = less.next_node
current = next_node
less.next_node = equal_head.next_node
equal.next_node = more_head.next_node
return less_head.next_node
# Tests:
a = ListNode.make_list([1, 2, 3, 1, 2, 3, 1, 2, 3])
b = pivot(a, 2)
print b.traversal()
a = ListNode.make_list([2, 2, 2, 3, 2, 2])
b = pivot(a, 2)
print b.traversal()
a = ListNode.make_list([1, 1, 1, 1, 1, 2, 1, 1, 1])
b = pivot(a, 2)
print b.traversal()
a = ListNode.make_list([1])
b = pivot(a, 2)
print b.traversal()
return False
def length(node):
if node is None: return 0
result = 0
current = node
while current:
current = current.next_node
result += 1
return result
# Tests:
from linked_list import ListNode
a = ListNode.make_list(range(15))
b = ListNode.make_list(range(6))
b_end = b.find(5)
a_mid = a.find(7)
b_end.next_node = a_mid
print "True", merges(a, b)
a = ListNode.make_list(range(15))
b = ListNode.make_list(range(6))
print "False", merges(a, b)
a = ListNode.make_list(range(15))
b = ListNode.make_list(range(6))
b_end = b.find(5)
a_mid = a.find(14)
b_end.next_node = a_mid
###
# Questions:
# Length of list
# Return type (assume none)
def remove_dupes(node):
current = node
while current:
succ = current.next_node
while succ and succ.value == current.value:
succ = succ.next_node
current.next_node = succ
current = succ
# Tests:
from linked_list import ListNode
a = ListNode.make_list(range(10))
remove_dupes(a)
print a.traversal()
a = ListNode.make_list([0, 1, 1, 1, 2, 2, 3, 4, 5, 5, 5, 5, 6, 6])
remove_dupes(a)
print a.traversal()
# Time: 4 minutes
###
# Mistakes / Bugs / Misses
###
# Forgot colon on line 14
def cyclic_shift(node, k):
# TODO: error checking
if k == 0: return
# Might as well use the "clever" solution
back = node
front = node
for _ in range(k):
front = front.next_node
while front.next_node:
back = back.next_node
front = front.next_node
new_head = back.next_node
back.next_node = None
front.next_node = node
return new_head
# Tests:
from linked_list import ListNode
a = ListNode.make_list(range(8))
b = cyclic_shift(a, 3)
print b.traversal(), "56701234"
# Time: 11 minutes
###
# Mistakes / Bugs / Misses
###
# screwed up doing the back/front pointers in the first loop
# line 28 had front.next_node = new_head, instead of node
even_current = even_current.next_node
else:
odd_current.next_node = current
odd_current = odd_current.next_node
on_even = not on_even
next_node = current.next_node
current.next_node = None
current = next_node
#current, current.next_node = current.next_node, None
odd_head = odd_head.next_node
even_head = even_head.next_node
even_current.next_node = odd_head
return even_head
# Tests:
a = ListNode.make_list(range(12))
result = even_odd(a)
print result.traversal()
a = ListNode.make_list(range(1))
result = even_odd(a)
print result.traversal()
# Time: 11 minutes
###
# Mistakes / Bugs / Misses
###
# Forgot lines 35 and 42
# Line 39 doesn't work for a reason I don't understand. (TODO: Card)
# Probably something about the assignment order?
###
# Problem
###
# Delete a node in a singly-linked list in O(1) time. You may modify
# the value field, and the node is not the last one in the list.
###
# Work
###
def delete_node(node):
node.value = node.next_node.value
node.next_node = node.next_node.next_node
# Tests
from linked_list import ListNode
a = ListNode.make_list(range(10))
node = a.find(6)
delete_node(node)
print a.traversal(), "6 deleted"
# Time: 2 minutes
###
# Mistakes / Bugs / Misses
###
def reverse(head):
prev = None
current = head
while current:
next_node = current.next_node
current.next_node = prev
prev = current
current = next_node
return prev
# Tests:
from linked_list import ListNode
a = ListNode.make_list([1, 2, 3, 4, 3, 2, 1])
print palindromic(a), "True"
print a.traversal()
a = ListNode.make_list([1, 2, 3, 3, 2, 1])
print palindromic(a), "True"
print a.traversal()
a = ListNode.make_list([1, 2, 3, 4, 2, 1])
print palindromic(a), "False"
print a.traversal()
a = ListNode.make_list([1])
print palindromic(a), "True"
print a.traversal()
while a or b or carry:
a_digit = a.value if a else 0
b_digit = b.value if b else 0
a = a.next_node if a else None
b = b.next_node if b else None
digit_sum = a_digit + b_digit + carry
new_digit = digit_sum % 10
carry = digit_sum / 10
result.next_node = ListNode(new_digit)
result = result.next_node
return result_head.next_node
# Tests:
a = ListNode.make_list([3, 1, 4])
b = ListNode.make_list([7, 0, 9])
result = add(a, b)
print result.traversal(), [0, 2, 3, 1]
a = ListNode.make_list([9, 9, 9, 9, 9, 9, 9])
b = ListNode.make_list([1])
result = add(a, b)
print result.traversal(), [0, 0, 0, 0, 0, 0, 0, 1]
b = ListNode.make_list([9, 9, 9, 9, 9, 9, 9])
a = ListNode.make_list([1])
result = add(a, b)
print result.traversal(), [0, 0, 0, 0, 0, 0, 0, 1]
b = ListNode.make_list([0])
def reverse(node):
current = node
previous = None
while current:
next_node = current.next_node
current.next_node = previous
previous = current
current = next_node
return (previous, node)
# Test
from linked_list import ListNode
a = ListNode.make_list([1, 2, 3, 4, 5])
result = reverse_sublist(a, 2, 4)
print result.traversal(), 14325
a = ListNode.make_list([1, 2, 3, 4, 5])
result = reverse_sublist(a, 2, 5)
print result.traversal(), 15432
a = ListNode.make_list([1, 2, 3, 4, 5])
result = reverse_sublist(a, 1, 5)
print result.traversal(), 54321
# Time: 17 minutes
###
# Mistakes / Bugs / Misses
while True:
slow = slow.next_node
fast = fast.next_node
if fast: fast = fast.next_node
if not fast: return None
if slow == fast: break
fast = head
while fast != slow:
slow = slow.next_node
fast = fast.next_node
return fast
# Test:
from linked_list import ListNode
ll = ListNode.make_list([1, 2, 3, 4, 5, 6, 7, 8])
start = ll.find(3)
end = ll.find(8)
end.next_node = start
result = cycle_test(ll)
print result == start, result, start
ll = ListNode.make_list(range(15))
start = ll.find(6)
end = ll.find(14)
end.next_node = start
result = cycle_test(ll)
print result == start, result, start
ll = ListNode.make_list(range(15))
result = cycle_test(ll)