1989번 백준

후위표기 stack

 
from sys import stdin
 
middle = stdin.readline()
back = []
ans =""
for m in middle:
  if m.isalpha():
    ans+=m
  else:
    if len(back) == 0:
      back.append(m)
    elif m == "(":
      back.append(m)
    elif m == "+" or m == "-":
      while True:
        if len(back)==0 or ( back[-1] == "("):
          break
        ans+=back.pop()
      back.append(m)
    elif m == "*" or m == "/":
      while True:
        if len(back)==0 or (back[-1] == "+" or back[-1] == "-" or back[-1] == "("):
          break
        ans+=back.pop()
      back.append(m)
    elif m == ")":
      while True:
        if back[-1] != "(":
          ans+=back.pop()
        else:
          back.pop()
          break
 
while len(back) !=0:
  ans+=back.pop()
 
 
print(ans)