function bookShelf(input) {
    let shelf = {};
    for (let line of input){
        if(line.includes("->")){
       let [iD, genre] = line.split(' -> ')
        if(shelf[iD] === undefined) shelf[iD] = {[genre]: [] };
    }else{
           let [bookName, genre] = line.split(", ")//
           for (let element in shelf){
             if(shelf[element].hasOwnProperty(genre))
             shelf[element][genre].push(bookName)
             }
            }
        }
        Object.keys(shelf).sort((a,b)=>Object.entries(shelf[b])[0][1].length - Object.entries(shelf[a])[0][1].length).forEach(el=>{
            console.log(`${el} ${Object.keys(shelf[el])}: ${Object.values(shelf[el])[0].length}`)

            Object.values(shelf[el]).map(x=>{x.sort((a,b)=> a.localeCompare(b)).map(el=> console.log(`--> ${el}`))
            })
        })
    }
bookShelf([
    "1 -> history",
    "1 -> action",
    "Death in Time: Criss Bell, mystery",
    "2 -> mystery",
    "3 -> sci-fi",
    "Child of Silver: Bruce Rich, mystery",
    "Hurting Secrets: Dustin Bolt, action",
    "Future of Dawn: Aiden Rose, sci-fi",
    "Lions and Rats: Gabe Roads, history",
    "2 -> romance",
    "Effect of the Void: Shay B, romance",
    "Losing Dreams: Gail Starr, sci-fi",
    "Name of Earth: Jo Bell, sci-fi",
    "Pilots of Stone: Brook Jay, history",
]);
console.log("----------------------");
bookShelf([
    "1 -> mystery",
    "2 -> sci-fi",
    "Child of Silver: Bruce Rich, mystery",
    "Lions and Rats: Gabe Roads, history",
    "Effect of the Void: Shay B, romance",
    "Losing Dreams: Gail Starr, sci-fi",
    "Name of Earth: Jo Bell, sci-fi",
]);