Discussion on: Daily Challenge #150 - Boggle Guess Validator

const getAllIdx = (arr, val) => {
    let indexes = [], i = -1;
    while ((i = arr.indexOf(val, i+1)) != -1){
        indexes.push(i);
    }
    return indexes;
}

const intersect = (a, b) => {
    const setA = new Set(a);
    const setB = new Set(b);
    const intersection = new Set([...setA].filter(x => setB.has(x)));
    return Array.from(intersection);
}

const range = (start, stop, step) => {
    const result = [];
    for (let i = start; i <= stop; i += step) {
        result.push(i);
    }

    return result;
}

const canBuildWord = (height, [first, second, ...rest], used=[]) => {
    let res = [];
    if (second === undefined) return true;

    for(let i = 0; i < first.length; i++) {

        nextUsed = [...used, first[i]];
        let val = first[i];
        ajacentIdx = [val-height, val+height];
        const rightBound = range(height-1, (height-1) + (height * (height-1)), height);
        const leftBound = range(0, height * height - 1, height);

        if (!rightBound.includes(val)) {
            ajacentIdx.push(val+1, val-height+1, val+height+1);
        }
        if (!leftBound.includes(val)) {
            ajacentIdx.push(val-1, val-height-1, val+height-1);
        }

        ajacentIdx = ajacentIdx.filter(x => !nextUsed.includes(x));

        let intersection = intersect(ajacentIdx, second);
        if (intersection.length === 0) {
            res.push(false);
        } else {
            for(let j = 0; j < intersection.length; j++) {
                res.push(canBuildWord(height, [intersection, ...rest], [...nextUsed, intersection[j]]));
            }
        }

    }
    return res.some(x => x);
}

const checkWord = (board, guess) => {
    const chars = guess.split('');
    const flat = [].concat.apply([], board);

    const startingPoints =[];
    for (let i = 0; i < chars.length; i++) {
        startingPoints.push(getAllIdx(flat, chars[i]));
    }

    const missingLetter = startingPoints.filter(points => points.length === 0).length !== 0;
    if (missingLetter) return false;

    return canBuildWord(board.length, startingPoints);
}