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# Day Eighteen: Operation Order
import std/[os, strutils]
let input = paramStr(1).readFile().strip().split("\n")
# cheese: add parenthesis and eval
func evaluate(a, b: int, op: char): int =
if op == '+':
return a + b
elif op == '*':
return a * b
else:
debugEcho "this should never happen."
return -1
var sum = 0
for line in input:
var stack: seq[tuple[val: int, op: char]] = @[(0, '+')]
for c in line:
let last = stack.len - 1
if c == ' ':
discard
elif c == '+' or c == '*':
stack[last].op = c
elif c == '(':
stack.add((0, '+'))
elif c == ')':
stack[last-1] = (evaluate(stack[last-1].val, stack.pop.val, stack[last-1].op), '+')
else:
stack[last] = (evaluate(stack[last].val, parseInt($c), stack[last].op), ' ')
sum += stack[stack.len - 1].val
echo sum
func shunting(expression: string): string =
var stack: seq[char]
for t in expression:
if t == ' ':
discard
elif t == '+':
while stack.len > 0 and stack[stack.len-1] == '+':
result.add(stack.pop)
stack.add(t)
elif t == '*':
while stack.len > 0 and (stack[stack.len-1] == '+' or stack[stack.len-1] == '*'):
result.add(stack.pop)
stack.add(t)
elif t == '(':
stack.add(t)
elif t == ')':
while stack.len > 0 and stack[stack.len - 1] != '(':
result.add(stack.pop)
assert stack.pop == '('
else:
result.add(t)
while stack.len != 0:
result.add(stack.pop)
func evaluate(expression: string): int =
var stack: seq[int]
for s in expression:
if s == ' ':
discard
elif s == '+':
stack.add(stack.pop + stack.pop)
elif s == '*':
stack.add(stack.pop * stack.pop)
else:
stack.add(parseInt($s))
assert stack.len == 1
return stack[0]
sum = 0
for line in input:
sum += evaluate(line.shunting())
echo sum
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