Day 1: Report RepairDay 2: Password PhilosophyDay 3: Toboggan TrajectoryDay 4: Passport ProcessingDay 5: Binary BoardingDay 6: Custom CustomsDay 7: Handy HaversacksDay 8: Handheld HaltingDay 9: Encoding ErrorDay 10: Adapter ArrayDay 11: Seating SystemDay 12: Rain RiskDay 13: Shuttle SearchDay 14: Docking DataDay 15: Rambunctious RecitationDay 16: Ticket TranslationDay 17: Conway CubesDay 19: Monster MessagesDay 25: Combo BreakerAdvent of Code Leaderboard 2020
Day 18: Operation Order
function tokenize(expression) {
return expression.split(/\b|\s/).map(t => t.trim()).flatMap(t => t.match(/[()]/) ? t.split('') : t)
}
evaluate(rpn('1 + 2'))
function* rpn(expression) {
const stack = []
for (const token of tokenize(expression)) {
switch (token) {
case '(':
stack.push(token)
break
case ')':
while (stack.length) {
const n = stack.pop()
if (n === '(')
break
yield n
}
break
case '+':
case '*':
if (stack.length === 0 || stack[stack.length-1] === '(') {
stack.push(token)
} else {
while (stack.length) {
if (stack[stack.length-1] === '(')
break
yield stack.pop()
}
stack.push(token)
}
break
default: // operand
yield +token
}
}
while (stack.length)
yield stack.pop()
}
function evaluate(rpn) {
const stack = []
for (const token of rpn) {
switch (token) {
case '+':
stack.push(stack.pop() + stack.pop())
break
case '*':
stack.push(stack.pop() * stack.pop())
break
default:
stack.push(token)
}
}
return stack[0]
}
part1 = input.trim().split('\n').map(rpn).map(evaluate).reduce((sum, i) => sum + i)
function* rpn2(expression) {
const stack = []
for (const token of tokenize(expression)) {
switch (token) {
case '(':
stack.push(token)
break
case ')':
while (stack.length) {
const n = stack.pop()
if (n === '(')
break
yield n
}
break
case '+':
case '*':
if (stack.length === 0 || stack[stack.length-1] === '(') {
stack.push(token)
} else {
while (stack.length) {
if (stack[stack.length-1] === '(' || (token === '+' && stack[stack.length-1] === '*'))
break
yield stack.pop()
}
stack.push(token)
}
break
default: // number
yield +token
}
}
while (stack.length)
yield stack.pop()
}
part2 = input.trim().split('\n').map(rpn2).map(evaluate).reduce((sum, i) => sum + i)
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