savings.js

savings.js

/*
--input.txt--
13 5 5
900 600 700 600 2000 2300 1600 500 2800 1500 1900 2200 2500
--EOF--
*/
process.stdin.resume();
process.stdin.setEncoding('utf8');
const LOG=true;
var stdin = '';
process.stdin.on('data', function (chunk) {
    stdin += chunk;
}).on('end', function() {
    var lines = stdin.trim().split('\n');
    let line0 = lines[0].split(' ').map(n => parseInt(n));
    let product_count = line0[0];
    let a_count = line0[1];
    let b_count = line0[2];
    let product_prices = lines[1].split(' ').map(n => parseInt(n)).sort((a, b) => {
        return b - a;
    });

    let prices = product_prices.map(pp => {
        let a = pp * 0.95;
        let b = pp >= 1000 ? pp - 100 : pp;
        let a_discount = pp - a;
        let b_discount = pp - b;
        return {price:pp, a, b, a_discount, b_discount, 
            coup : a_discount > b_discount ? 'a' : 'b',
            used : '',
        };
    });
    prices.sort((p, q) => q.price - p.price);

    // output
    let pay = 0;

    // all B coupons
    let b_used = 0;
    LOG && console.log('== phase 1 : use up all B coupons ==');
    prices.filter(p => p.used === '').filter(p => p.coup === 'b').forEach(p => {
        if (! b_count) return;
        b_count--;
        LOG && console.log('using B on :' , JSON.stringify(p), ' ... saves $', p.b_discount );

        pay += p.b;
        p.used ='b';
        b_used++;
    });
    LOG && console.log(`used ${b_used} B coupons ; got ${b_count} more B coupons`);


    let a_used = 0;
    function use_a_coupons() {
        prices.filter(p => p.used === '').sort((p, q)=>q.a_discount - p.a_discount).forEach(p => {
            if (! a_count) return;
            a_count--;
           LOG &&  console.log('using A on :' , JSON.stringify(p), ' ... saves $', p.a_discount );

            pay += p.a;
            p.used ='a';
            a_used++;
        });
    }

    LOG && console.log('== phase 2 : use up all A coupons ==');
    use_a_coupons();

    if (b_count) {
        let prices_old = JSON.parse(JSON.stringify(prices));
        let pay_old = pay;

        LOG && console.log('== phase 3 : sacrifice some A==');
        // reverse some A coupon usage; starting from the product with least savings
        prices.filter(p => p.used === 'a' && p.b_discount).sort((p, q)=>p.a_discount - q.a_discount).forEach(p => {
            if (! b_count) return;
            LOG && console.log('using B instead of A on :' , JSON.stringify(p), ' ... saves $', p.b_discount, 'using B , instead of $', p.a_discount);
            pay -= p.a;

            p.used = 'b';
            pay += p.b;

            b_used++;
            b_count--;

            a_used--;
            a_count++;
        });

        use_a_coupons();

        // examine whether we have saved money 
        function pay_how_much(price_list) {
            let out = 0;
            price_list.forEach(p => {
                out += p.used === 'a' ? p.a : p.used ==='b' ? p.b : p.price; 
            });
            return out;
        }

        let pay_pre = pay_how_much(prices_old);
        let pay_new = pay_how_much(prices);

        if (pay_new < pay_pre) {
            console.log(`after swapping coupons, we're paying ${pay_new} instead of ${pay_pre} (total of $ ${pay_pre - pay_new} extra savings!)`);
        }
        else {
            console.log('we are better off not swapping coupons');
            pay = pay_old;
            prices = prices_old;
        }

    }



    LOG && console.log('== phase 4 : full price ==');

    prices.filter(p => p.used === '').forEach(p => {
        LOG && console.log('paying full price :', JSON.stringify(p));
        pay += p.price;
    });


    LOG && console.log('== conclusion ==');
    LOG && console.log(`we have ${a_count} A coupons unused; ${b_count} B coupons unused`);
    console.log(pay);





});