function missingNumbers(arr: number[], brr: number[]): number[] {
    // convert all of arr to arrMap
    const arrMap = new Map();
    let shifted;
    while(arr.length){
        shifted = arr.shift();
        arrMap.set(shifted, (arrMap.get(shifted) || 0) + 1);
    }
    const diff = new Set<number>();
    
    // remove any brr that matches in arrMap,
    // then remove from arrMap and brr
    // any non matches, save in diff
    while(brr.length){
        shifted = brr.shift();
     if (arrMap.has(shifted)) {
        arrMap.set(shifted, arrMap.get(shifted) - 1);
        if (arrMap.get(shifted) === 0) {
            arrMap.delete(shifted);
        }
     } else {
        diff.add(shifted);
     }
    }
    // diff is prefiltered and just needs to be sorted
    return Array.from(diff).sort((a, b) => a - b);
}