Discussion on: AoC Day 15: Beverage Bandits

[Tiago Romero Garcia]

JavaScript solution

After about 20 hours (distributed over 4 days) I finally got this one! I didn't give up, it felt like a real-life project, requiring research and intensive debugging, and after so much effort, it was SOOO satisfying to see it running.!

For me, Part 1 executed in 3 minutes, and Part 2 took 54 minutes!!!

I would be more than happy to answer questions and give tips about that, but basically I really thank @neilgall for his fantastic explanation and the usage of Dijkstra's algorithm.

I'm gonna omit reader.js which is the same as the other solutions and jump to the point:

15-common.js

const MAP = {
    WALL: '#',
    CAVERN: '.',
    GOBLIN: 'G',
    ELF: 'E'
};

const ENEMIES = {
    [MAP.GOBLIN]: MAP.ELF,
    [MAP.ELF]: MAP.GOBLIN
}

const MAX_HP = 200;
const INITIAL_AP = 3;

let generator = 0;
class Square {
    constructor({x, y, type}) {
        this.x = x;
        this.y = y;
        this.type = type;

        if ([MAP.GOBLIN, MAP.ELF].includes(type)) {
            this.unit = {
                id: generator++,
                type,
                square: this,
                enemyOf: ENEMIES[type],
                hp: MAX_HP,
                ap: INITIAL_AP,
                isAlive: true
            }
        }
    }
}

const readDungeon = lines => {
    const n = lines.length;

    const dungeon = Array.from({ length: n }, row => []);

    const units = [];
    for (let i = 0; i < n; i++) {
        let m = lines[i].indexOf(' ');
        m = m === -1 ? lines[i].length : m;
        for (let j = 0; j < m; j++) {
            const square = dungeon[i][j] = new Square({x: i, y: j, type: lines[i][j]});
            if (square.unit) {
                units.push(square.unit);
            }
        }
    }

    return { dungeon, units };
};

const getAdjacents = (dungeon, square, type) => {
    const n = dungeon.length;
    const m = dungeon[0].length;

    const { x, y } = square;
    const adjacents = [];
    if (x > 0) adjacents.push(dungeon[x-1][y]);
    if (y > 0) adjacents.push(dungeon[x][y-1]);
    if (y < m - 1) adjacents.push(dungeon[x][y+1]);
    if (x < n - 1) adjacents.push(dungeon[x+1][y]);

    return type ? adjacents.filter(square => square.type === type) : adjacents;
}

const getKey = ({ x, y }) => `${x},${y}`;

const getMinimumDistance = (dungeon, start, end) => {
    const unvisitedSquares = new Set();
    const distances = new Map();
    const getDistance = square => distances.get(getKey(square));

    // Setting initial infinite distances
    const n = dungeon.length;
    const m = dungeon[0].length;
    for (let i = 0; i < n; i++) {
        for (let j = 0; j < m; j++) {
            const square = dungeon[i][j];
            if (square.type === MAP.CAVERN) {
                distances.set(getKey(square), Number.POSITIVE_INFINITY);
                unvisitedSquares.add(square);
            }
        }
    }

    distances.set(getKey(start), 0);

    let current = start;
    while (current) {
        const nextDistance = getDistance(current) + 1;
        getAdjacents(dungeon, current, MAP.CAVERN)
            .filter(square => unvisitedSquares.has(square))
            .forEach(square => distances.set(getKey(square), Math.min(getDistance(square), nextDistance)));

        unvisitedSquares.delete(current);

        current = unvisitedSquares.size > 0 ?
            [...unvisitedSquares].reduce((minimum, square) => getDistance(minimum) <= getDistance(square) ? minimum : square) :
            undefined;
    }

    const endDistance = Math.min(...getAdjacents(dungeon, end, MAP.CAVERN).map(getDistance));

    return { endDistance, getDistance };
};

const getNext = (dungeon, unit, nearest) => {
    const { endDistance, getDistance } = getMinimumDistance(dungeon, nearest, unit);
    return getAdjacents(dungeon, unit, MAP.CAVERN).find(square => getDistance(square) === endDistance);
};

const step = (unit, nearest) => {
    const oldSquare = unit.square;
    delete oldSquare.unit;
    oldSquare.type = MAP.CAVERN;

    nearest.unit = unit;
    nearest.type = unit.type;
    unit.square = nearest;
};

const move = (unit, units, enemies, openCaverns, dungeon) => {  
    const allReachables = [];  
    for (let enemy of enemies) {
        const adjacents = getAdjacents(dungeon, enemy.square, MAP.CAVERN);
        const inRange = adjacents.map(square => {
            return {
                square,
                distance: getMinimumDistance(dungeon, square, unit.square).endDistance
            };
        });
        const reachables = inRange.filter(adjacent => adjacent.distance < Number.POSITIVE_INFINITY);
        allReachables.push(...reachables);
    }

    if (allReachables.length > 0) {
        const nearest = allReachables.reduce((nearest, square) => nearest.distance <= square.distance ? nearest : square);
        const next = getNext(dungeon, unit.square, nearest.square);

        step(unit, next);
    }
}

const attack = (unit, enemiesInRange) => {
    const minHp = enemiesInRange.reduce((min, enemy) => Math.min(min, enemy.hp), MAX_HP);
    const weakestEnemy = enemiesInRange.filter(({hp}) => hp === minHp)[0];

    weakestEnemy.hp -= unit.ap;

    if (weakestEnemy.hp <= 0) {
        weakestEnemy.isAlive = false;
        weakestEnemy.square.type = MAP.CAVERN;
        delete weakestEnemy.square.unit;
        delete weakestEnemy.square;
    }    
}

const getEnemiesInRange = (adjacents, { enemyOf }) => {
    return adjacents
        .filter(square => square.type === enemyOf && square.unit)
        .map(square => square.unit);
};

const sort = units => {
    units.sort((a, b) => {
        const sA = a.square;
        const sB = b.square;
        return (sA.x === sB.x) ? sA.y - sB.y : sA.x - sB.x;
    });
};

const makeRound = (dungeon, units) => {
    const n = dungeon.length;
    const m = dungeon[0].length;

    let hasCombatEndedEarly = false;
    for (let unit of units) {
        if (unit.isAlive) {
            // If no enemies, combat ends early
            const hasEnemies = units.some(enemy => enemy.type === unit.enemyOf && enemy.isAlive);
            if (hasEnemies) {
                // Determine action
                let adjacents = getAdjacents(dungeon, unit.square);
                let enemiesInRange = getEnemiesInRange(adjacents, unit);

                if (enemiesInRange.length === 0) {
                    // Moves and attacks
                    const openCaverns = adjacents.filter(square => square.type === MAP.CAVERN);
                    const enemies = units.filter(nextUnit => unit.enemyOf === nextUnit.type && nextUnit.isAlive);
                    if (openCaverns.length > 0 && enemies.length > 0) {
                        // Moves
                        move(unit, units, enemies, openCaverns, dungeon);

                        // Attacks
                        adjacents = getAdjacents(dungeon, unit.square);
                        enemiesInRange = getEnemiesInRange(adjacents, unit);
                        if (enemiesInRange.length > 0) {
                            attack(unit, enemiesInRange);
                        }
                    }
                }
                else {
                    // Attacks
                    attack(unit, enemiesInRange);
                }
            }
            else {
                hasCombatEndedEarly = true;
            }
        }
    }

    // Removes dead
    while (units.some(unit => !unit.isAlive)) {
        const nextDead = units.find(unit => !unit.isAlive);
        units.splice(units.indexOf(nextDead), 1);
    }

    sort(units);

    return hasCombatEndedEarly;
};

const getOutcome = (rounds, units) => {
    const remainingHp = units.reduce((total, unit) => total += unit.hp, 0);
    return rounds * remainingHp;
};

const getGoblins = units => units.filter(unit => unit.type === MAP.GOBLIN);
const getElves = units => units.filter(unit => unit.type === MAP.ELF);

const printStats = (rounds, dungeon, units) => {
    console.log(`round ${rounds}:`);
    console.log(dungeon.map(row => row.map(col => col.type).join('')).join('\n'));
    console.log(units.map(u => `${u.type}(${u.id}): ${u.hp}`));        
}

module.exports = {
    readDungeon,
    makeRound,
    getGoblins,
    getElves,
    printStats,
    getOutcome  
};

15a.js

const { readFile } = require('./reader');
const {
    readDungeon,
    makeRound,
    getGoblins,
    getElves,
    printStats,
    getOutcome  
} = require('./15-common');

(async () => {
    const lines = await readFile('15-input.txt');

    const { dungeon, units } = readDungeon(lines);

    let goblins, elves, rounds = 0;
    do {
        const hasCombatEndedEarly = makeRound(dungeon, units);
        if (!hasCombatEndedEarly) rounds++;

        goblins = getGoblins(units).length;
        elves = getElves(units).length;

        printStats(rounds, dungeon, units);
    } while (goblins > 0 && elves > 0);

    console.log(`The ${goblins > 0 ? 'goblins': 'elves'} won!`);
    console.log(`The outcome of the combat is ${getOutcome(rounds, units)}`);
})();

15b.js

const { readFile } = require('./reader');
const {
    readDungeon,
    makeRound,
    getElves,
    getGoblins,
    printStats,
    getOutcome  
} = require('./15-common');



(async () => {
    const lines = await readFile('15-input.txt');

    let ap = 3;
    let areAllElvesAlive;
    do {
        ap++;
        console.log(`\nWith AP as ${ap}:`);

        const { dungeon, units } = readDungeon(lines);
        const elves = getElves(units);
        elves.forEach(elf => elf.ap = ap);

        let initialElvesCount = elves.length;
        let elvesCount, goblinsCount;

        let rounds = 0;
        do {
            console.log(`AP ${ap}, round ${rounds+1}`);
            const hasCombatEndedEarly = makeRound(dungeon, units);
            if (!hasCombatEndedEarly) rounds++;            

            goblinsCount = getGoblins(units).length;
            elvesCount = getElves(units).length;
            areAllElvesAlive = elvesCount === initialElvesCount;
        } while (areAllElvesAlive && goblinsCount > 0);

        printStats(rounds, dungeon, units);

        if (areAllElvesAlive) {
            console.log(`\nAll elves survived when AP is ${ap}`);
            console.log(`The outcome of the last combat is ${getOutcome(rounds, units)}`);
        }
        else {
            console.log(`There was an elf casualty!`);
        }        
    } while (!areAllElvesAlive);    
})();

[Ryan Palo]

Awesome! Really nice work!

[Javid Asgarov]

Is your path finding algorithm the dijkstra one? Thanks, it was very clear how it works, maybe because it in javascript :), I used it for my solution for part one.

But I didn't understand how you choose the next step exactly. It works, but I can't see where you break the ties in reading order. Anyhow, nicely done, learned how to find shortest route with your code.

[Tiago Romero Garcia]

Hi @askeroff , thanks!! Yes, I'm using Dijkstra's algorithm (even though I didn't explicitly mention it in the code), but it's implemented on getMinimumDistance function, where I basically do the following steps to get the minimum step between "start" and "end" squares:

1. create a map for the distances of all squares and set each one of them as Number.POSITIVE_INFINITY
2. create a set to mark unvisited squares and add every square to it
3. set "current" as the unvisited square with the lowest distance (or the "start" square in the beginning)
4. for each unvisited unblocked neighbors of "current", update the distance to the minimum between distance(current)+1 and the neighbor's current distance.
5. mark "current" as visited (by removing it from the unvisited squares set)
6. go back to step 3 and repeat until there are no more unvisited squares

The final distance between "start" and "end" is the smallest distance of all "end"'s unblocked neighbors.

[Tiago Romero Garcia]

Also, to break the ties in the reading order, it's all in getAdjacents function, where I look for the following neighbor squares and return in their reading order.

Considering we're getting adjacents for position X,Y, N=max(X) and M=max(Y)

1. if X > 0, adjacent on X-1,Y
2. if Y > 0, adjacent on X,Y-1
3. if Y < M-1, adjacent on X,Y+1
4. if X < N-1, adjacent on X+1,Y

In other words,

1. Neighbor on the line above
2. Neighbor on the same line, to the left
3. Neighbor on the same line, to the right
4. Neighbor on the line below

[Javid Asgarov]

Oh, awesome. I got it. I want to come back after I've done others and revisit this problem with breadth-first-search. Maybe it'll be faster.