Challenge 3
- Algorithms course
- Beginner
- Lesson 79/80
- 4 min
Sort an array with bubble sort and print it.
Challenge 3: Stack with parentheses
In this challenge you will balance parentheses using a stack. Every opened parenthesis must be closed.
String: '(())' is balanced, '(()' is not. Push open parens, pop on close.
Practice Balance parentheses
Write balance_parens(s). Balance with a stack, return True if balanced. Print True with print(balance_parens('(())')).
Starter code
def balance_parens(s):
# Balance parenthesesSample solution
def balance_parens(s):
# Balance parentheses
stack = []
for ch in s:
if ch == '(':
stack.append(ch)
elif ch == ')':
if len(stack) == 0:
return False
stack.pop()
return len(stack) == 0
print(balance_parens('(())'))Expected output
True
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Challenge 3: match the terms
| Term | Meaning |
|---|---|
stack |
Parenthesis |
push |
Open paren |
pop |
Close paren |
empty |
Balanced |
2 Which parenthesis string is balanced?
- (()
- ())(
- )(
- (()) Correct answer
Explanation: (()) is balanced.
3 Balanced
Question
A balanced stack is ____ at the end.
Answer
A balanced stack is empty at the end.Explanation: empty is right.