Mask Network Front-end Interview Problem Set Answers.md

Problem 0

type GetLastElementType<T extends any[]> = T[2]

NOTE: There might be a way to pick the type of the last item in an array of any length, but I didn't know.

Problem 1

function toGetterSetter<T extends Record<string, any>, K extends keyof T>(dict: T):
    { [U in K as `get_${U & string}`]: () => T[U] } &
    { [V in K as `set_${V & string}`]: (v: T[V]) => void; }
{
    const getterSetter = {} as any;
    for (const [k, v] of Object.entries(dict)) {
        getterSetter[`get_${k}`] = () => v;
        getterSetter[`set_${k}`] = (v: any) => (dict as any)[k] = v;
    }
    return getterSetter;
}

Problem 2

const STATE = {
    AL: 'AL', // Alabama
    AK: 'AK', // Alaska
    AZ: 'AZ', // Arizona
    AR: 'AR', // Arkansas
} as const;

const STATE_DATA: Record<string, { [K in keyof typeof STATE]: any }> = {
    POST_CODE: {
        [STATE.AL]: '01',
        [STATE.AK]: '02',
        [STATE.AZ]: '03',
        [STATE.AR]: '04',
    },
    AREA: {
        [STATE.AL]: 100,
        [STATE.AK]: 200,
        [STATE.AZ]: 300,
        [STATE.AR]: 400,
    },
    CITIES: {
        [STATE.AL]: ['city 1', 'city 2'],
        [STATE.AK]: ['city 3', 'city 4'],
        [STATE.AZ]: ['city 5', 'city 6'],
        [STATE.AR]: ['city 7', 'city 8'],
    }
};

function getStateData<D extends typeof STATE_DATA, K extends keyof D>(data: D[K], state: keyof typeof STATE) {
    return data[state]
}

// use cases
getStateData(STATE_DATA.POST_CODE, STATE.AL) // 01
getStateData(STATE_DATA.AREA, STATE.AL) //  100 
getStateData(STATE_DATA.CITIES, STATE.AZ) // ['city 7', 'city 8']