Stack Discipline Target: 15s
Stack-based expression evaluation is the foundation for calculator and RPN problems.
for tok in tokens:
if tok.lstrip('-').isdigit():
stack.append(int(tok))
else:
b, a = stack.pop(), stack.pop()
if tok == '+': stack.append(a + b)
elif tok == '-': stack.append(a - b)
elif tok == '*': stack.append(a * b)
elif tok == '/': stack.append(int(a / b))Type it from memory. Go.