PW_15

Basics

from stack import stack

gerard = stack()
gerard.push(1)
gerard.push(2)
gerard.push(4)
print(gerard)
gerard.pop()
gerard.push(3)
print(gerard)

def stackOfList(tab: list) -> stack:
    st = stack()
    for e in tab:
        st.push(e)
    return st

Positive Stack

I used @overload to have two functions with the same name. I do believe this is not the right syntax, but I can't find the right python docs for that.

from typing import overload
from stack import stack

@overload
def positive(tab: list) -> stack:
    st = stack()
    for e in tab:
        if e >= 0:
            st.push(e)
    return st

@overload
def positive(s: stack) -> stack:
    st = stack()
    tmp = stack()
    while not s.is_empty():
        e = s.pop()
        tmp.push(e)
    while not tmp.is_empty():
        e = tmp.pop()
        s.push(e)
        if e >= 0:
            st.push(e)

    return st

positive([])
positive(stack())

Parentheses

from typing import overload
from stack import stack

def parentheses(p : string) -> bool:
    st = stack()
    for c in p:
        if c == "(":
            st.push(1)
        elif c == ")":
            if st.is_empty():
                return False
            else:
                st.pop()
    
    if st.is_empty():
        return True
    return False


assert parentheses("((()())(()))") == True, "Case True"
assert parentheses("())(()") == False, "Case too soon"
assert parentheses("(())(()") == False, "Case too late"

Postfix

from stack import stack

def eval_postfix(tab : list) -> float:
    st = stack()
    r = 0
    for e in tab:
        print(e)
        if e == "+":
            while not st.is_empty():
                r += st.pop()
        elif e == "-":
            while not st.is_empty():
                r -= st.pop()
        elif e == "*":
            while not st.is_empty():
                r *= st.pop()
        elif e == "/":
            while not st.is_empty():
                r /= st.pop()
        else:
            st.push(e)
    
    return r

print(eval_postfix([2, 3, '+', 5, '*']))