Super important to overdose on the debugger for these sorts of exercises in order to fully apprehend how to use Objects and Arrays with JS. Especially so, since during the Advanced + Web modules, no further time will be spent on them and the focus will be turned on Node, Mongo, DOM ...

;-)

function solve(input) {
    let result = {};

    input.map(x => {
        let [country, town, price] = x.split(' > ');

        // if (x[country] === undefined) {
        if (!result.hasOwnProperty(country)) {
            // x[country] = {};
            result[country] = {};
        }

        if (!result[country].hasOwnProperty(town)) {
            result[country][town] = Number(price);
        } else if (result[country][town] > Number(price)) {
            result[country][town] = Number(price);
        }

        // if (x[country][town] === undefined) {
        //     x[country][town] = Number(price);

        //     if (x[town][price] > Number(price))
        //         x[town][price] = Number(price);
        // }
    });

    let sorted = Object.entries(result).sort((a, b) => a[0].localeCompare(b[0]));
    sorted.forEach(([country, towns]) => {
        // console.log(`${x[0]} -> ${x[1]} -> ${x[2]}`)
        let finalString = `${country} -> `;
        let sortedTowns = Object.entries(towns).sort((a, b) => a[1] - b[1]);
        sortedTowns.forEach(([town, price]) => {
            finalString += `${town} -> ${price} `;
        });

        console.log(finalString.trim());
    });
}