A12 - Printer

atcoder.jp

1 ≦ Ai ≦ 10,000,000,000 なので、A1 = 1, A2 = 2, ... Ai = i になる、か？一応正解したけど腑に落ちていない。

var NK = Console.ReadLine()!.Split(" ").Select(x => long.Parse(x)).ToList();
var N = NK[0];
var K = NK[1];
var A = Console.ReadLine()!.Split(" ").Select(x => long.Parse(x)).ToList();

var leftSecond = 1L;
var rightSecond = 10_000_000_000L;
while (leftSecond < rightSecond)
{
    var middleSecond = (leftSecond + rightSecond) / 2;
    if (Check(middleSecond))
    {
        rightSecond = middleSecond;
    }
    else
    {
        leftSecond = middleSecond + 1;
    }
}

Console.WriteLine(rightSecond);

bool Check(long second)
{
    var sum = A.Sum(a => second / a);
    return sum >= K;
}