def longest_valid_parens(string):
stack = Stack()
longest = 0
for c in string:
if c == '(':
stack.push(c)
elif c == ')':
if not stack.empty():
top = stack.pop()
if top == '(':
longest += 2
return longest
def evaluate_with_stack(rpn):
stack = Stack()
stack.push(int(rpn[0]))
for i in rpn[1:]:
if i in operators:
y = stack.pop()
x = stack.pop()
result = operators[i](x, y)
stack.push(result)
else:
stack.push(int(i))
assert(stack.size() == 1)
result = stack.pop()
return result
def shortest_transformation(start, end, dict):
assert(len(start) == len(end))
dict.append(end)
root = Node(start, None, 1)
stack = Stack()
stack.push(root)
char_list = []
for i in range(0, len(start)):
char_list.append(set([word[i] for word in dict]))
added_to_stack = [start]
while not stack.empty():
top = stack.pop()
original_str = top.data
num_transformations = top.transformations + 1
for i in range(0, len(original_str)):
for c in char_list[i]:
new_str = original_str
new_str = new_str.replace(new_str[i], c)
if new_str == original_str:
continue
if new_str == end:
# figure out the transformations
transformations = [new_str]
node = top
while node.parent is not None:
transformations.append(node.data)
node = node.parent
transformations.append(start)
transformations.reverse()
print(" --> ".join(transformations))
return num_transformations
if new_str in dict:
if new_str not in added_to_stack:
n = Node(new_str, top, num_transformations)
stack.push(n)
added_to_stack.append(new_str)
return 0, []
def shortest_transformation(start, end, dict):
assert len(start) == len(end)
dict.append(end)
root = Node(start, None, 1)
stack = Stack()
stack.push(root)
char_list = []
for i in range(0, len(start)):
char_list.append(set([word[i] for word in dict]))
added_to_stack = [start]
while not stack.empty():
top = stack.pop()
original_str = top.data
num_transformations = top.transformations + 1
for i in range(0, len(original_str)):
for c in char_list[i]:
new_str = original_str
new_str = new_str.replace(new_str[i], c)
if new_str == original_str:
continue
if new_str == end:
# figure out the transformations
transformations = [new_str]
node = top
while node.parent is not None:
transformations.append(node.data)
node = node.parent
transformations.append(start)
transformations.reverse()
print(" --> ".join(transformations))
return num_transformations
if new_str in dict:
if new_str not in added_to_stack:
n = Node(new_str, top, num_transformations)
stack.push(n)
added_to_stack.append(new_str)
return 0, []
def longest_valid_parens(string):
stack = Stack()
longest = 0
for c in string:
if c == '(':
stack.push(c)
elif c == ')':
if not stack.empty():
top = stack.pop()
if top == '(':
longest += 2
return longest
def has_valid_parens(string):
stack = Stack()
closing_ops = [')','}',']']
open_ops = ['(', '{', '[']
open_close_dict = {
'(': ')',
'{': '}',
'[': ']',
}
for c in string:
if c in closing_ops:
top = stack.pop()
if open_close_dict[top] != c:
return False
elif c in open_ops:
stack.push(c)
return stack.empty()
def evaluate_with_stack(rpn):
stack = Stack()
stack.push(int(rpn[0]))
for i in rpn[1:]:
if i in operators:
y = stack.pop()
x = stack.pop()
result = operators[i](x, y)
stack.push(result)
else:
stack.push(int(i))
assert (stack.size() == 1)
result = stack.pop()
return result
