Basic Calculator II — LeetCode 227 Python Solution
MediumStackMathString
- Problem
- #227
- Pattern
- Stack
- Reading time
- 4 min
- Source
- leetcode.com
The problem
Given a string s which represents an expression, evaluate this expression and return its value. The integer division should truncate toward zero.
Example
- Input
- s = "3+2*2"
- Output
- 7
Python solution
Python
class Solution:
def calculate(self, s: str) -> int:
v, n = 0, len(s)
sign = '+'
stk = []
for i, c in enumerate(s):
if c.isdigit():
v = v * 10 + int(c)
if i == n - 1 or c in '+-*/':
match sign:
case '+':
stk.append(v)
case '-':
stk.append(-v)
case '*':
stk.append(stk.pop() * v)
case '/':
stk.append(int(stk.pop() / v))
sign = c
v = 0
return sum(stk)Complexity
| Measure | Complexity |
|---|---|
| Time | O(n) |
| Space | O(n), where n is the length of the string s auxiliary |
Pattern: Stack
When the most recent unresolved thing is the one that matters, use a stack. LeetCode 227. Basic Calculator II is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Stack.
The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.
Related problems
Frequently asked questions
- How hard is LeetCode 227. Basic Calculator II?
- LeetCode 227. Basic Calculator II is rated Medium on LeetCode.
- What is the time complexity of LeetCode 227. Basic Calculator II?
- The Python solution on this page runs in O(n).
- What is the space complexity of LeetCode 227. Basic Calculator II?
- The Python solution on this page uses O(n), where n is the length of the string s auxiliary space.
- What topics does LeetCode 227. Basic Calculator II cover?
- LeetCode 227. Basic Calculator II is tagged Stack, Math and String on LeetCode.