AoC2020_Day18.py

expr = inp.split('\n')

# PART 1

# expr is a simple expression that has no parentheses
def evaluate(expr, part=1):
  if part == 2:
    if expr.find('(') > -1:
      return [str(eval(expr))]
    else:
      expr = ' '.join(addParentsAroundAddition(expr.split(' ')))
      return [str(eval(expr))]

  expr = expr.replace('(','')
  expr = expr.replace(')', '')
  splitExpr = expr.split(' ')
  while len(splitExpr) > 1:
    partialResult = None
    for x in range(len(splitExpr)):
      if not splitExpr[x].isdigit():
        operand = splitExpr[x]
        left = splitExpr[x - 1]
        right = splitExpr[x + 1]
        partialResult = eval(left + operand + right)
        break
    if partialResult:
      splitExpr = [str(partialResult)] + splitExpr[3:]

  return splitExpr

# Find the inner most parentheses
def innerParentheses(expr, part=1):
  pIndex = []
  parentheses = []
  mostRecent = ''
  hasParen = False
  for x in expr:
    if x == '(':
      hasParen = True
      break
  if hasParen:
    for x in range(len(expr)):
      if expr[x] == '(':
        if mostRecent != '(':
          pIndex.append(x)
          mostRecent = '('
        else:
          pIndex = [x]
      else:
        if expr[x] == ')' and mostRecent == '(':
          pIndex.append(x)
          mostRecent = ''
      if (len(pIndex) == 2):
        parentheses.append(pIndex)
        if part == 1:
          expr = expr[:pIndex[0]] + evaluate(''.join(expr[pIndex[0] + 1:pIndex[1]])) + expr[pIndex[1] + 1:]
        else:
          expr = expr[:pIndex[0]] + evaluate(' '.join(addParentsAroundAddition(''.join(expr[pIndex[0] + 1:pIndex[1]]).split(' '))), 2) + expr[pIndex[1] + 1:]
        return innerParentheses(expr, part)
        pIndex = []
  return expr

res = 0
for x in expr:
  res += int(evaluate(''.join(innerParentheses(list(x))))[0])

print(res)

# PART 2
# Addition should be evaluated before multiplication

def getAdditionIndices(expr):
  indices = []
  for x in range(len(expr)):
    if expr[x] == '+':
      indices.append(x)
  return indices

def addParentsAroundAddition(expr):
  additionIndices = getAdditionIndices(expr)
  for x in range(len(expr)):
    if x in additionIndices:
      expr[x - 1] = '(' + expr[x - 1]
      expr[x + 1] += ')'
  return expr

res = 0
for x in expr:
  res += int(evaluate(''.join(innerParentheses(list(x), 2)), 2)[0])

print(res)