136 lines
3.1 KiB
JavaScript
136 lines
3.1 KiB
JavaScript
// turn: 0-1; 1 bit (0 = player 1; 1 = player 2)
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// pos1: 1-10; 4 bits
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// pos2: 1-10; 4 bits
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// score1: 0-1009; 10 bits
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// score2: 0-1009; 10 bits
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const sizeS = 10
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const sizeP = 4
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const sizeT = 1
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const maskS = (1 << sizeS) - 1
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const maskP = (1 << sizeP) - 1
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const maskT = (1 << sizeT) - 1
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const offsetS2 = 0
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const offsetS1 = offsetS2 + sizeS
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const offsetP2 = offsetS1 + sizeS
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const offsetP1 = offsetP2 + sizeP
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const offsetT = offsetP1 + sizeP
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function encodeState(turn, pos1, pos2, score1, score2) {
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return (score2 << offsetS2) |
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(score1 << offsetS1) |
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(pos2 << offsetP2) |
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(pos1 << offsetP1) |
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(turn << offsetT)
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}
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function getScore(state, player) {
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return state >> (player ? offsetS2 : offsetS1) & maskS
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}
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function advState(state, roll, win) {
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let turn = state >> offsetT
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let offsetPos = turn ? offsetP2 : offsetP1
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let offsetScore = turn ? offsetS2 : offsetS1
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let pos = (state >> offsetPos) & maskP
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let score = (state >> offsetScore) & maskS
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pos = (((pos + roll) - 1) % 10) + 1
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score += pos
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if (score >= win) {
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return turn
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}
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state &= ~(maskP << offsetPos)
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state |= pos << offsetPos
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state &= ~(maskS << offsetScore)
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state |= score << offsetScore
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state ^= 1 << offsetT
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return state
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}
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const rollCombos = [1, 2, 3].cartProduct([1, 2, 3]).cartProduct([1, 2, 3]).map((e) => e.flat().sum())
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function day21(input, part2) {
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let lines = input.split("\n")
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let pos1 = +lines[0].split(" ").last
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let pos2 = +lines[1].split(" ").last
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let state = encodeState(0, pos1, pos2, 0, 0)
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if (!part2) {
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const win = 1000
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let die = 0
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let rolls = 0
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while (getScore(state, 0) < win && getScore(state, 1) < win) {
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let roll = ++die
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die %= 100
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roll += ++die
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die %= 100
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roll += ++die
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die %= 100
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rolls += 3
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newState = advState(state, roll, win)
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if (newState == 0 || newState == 1) {
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return getScore(state, 1 - newState) * rolls
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}
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state = newState
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}
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} else {
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let universes = {}
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universes[state] = 1
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let wins = [0, 0]
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while (true) {
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let universesLeft = false
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for (let state in universes) {
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if (!universes[state]) {
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continue
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}
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universesLeft = true
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state = +state
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for (let roll of rollCombos) {
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let newState = advState(state, roll, 21)
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if (newState == 0 || newState == 1) {
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wins[newState] += universes[state]
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} else {
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universes[newState] = (universes[newState] || 0) + universes[state]
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}
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}
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delete universes[state]
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}
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if (!universesLeft) {
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break
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}
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}
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return wins.max()
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}
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}
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if (typeof window == "undefined") {
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module.exports = day21
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}
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