Problem can be found in here!
Solution: Stack
def calculate(s: str) -> int:
number = 0
prev_operator = "+"
s += "+"
stack = []
for char in s:
if char.isdigit():
number = number*10 + int(char)
elif char == " ":
continue
else:
if prev_operator == "+":
stack.append(number)
elif prev_operator == "-":
stack.append(-number)
elif prev_operator == "*":
stack.append(number * stack.pop())
else:
stack.append(int(stack.pop() / number))
number, prev_operator = 0, char
return sum(stack)Time Complexity: , Space Complexity: