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Factory Production Time

Find the earliest time parallel machines can finish a target number of items.

Чему вы научитесь

  • Binary search over time instead of items
  • Check if a time is enough in one pass
  • Pick safe search bounds

Условие

Показать перевод

All machines start at time 0 and work independently. A machine with time t finishes one item after t seconds, another after 2t seconds, and so on. Find the earliest whole second when their combined production reaches the target.

Implement factory_machines(times, target).

Input

times: Seconds needed for one item on each machine.

target: The number of completed items required.

Output

Return the minimum elapsed seconds.

Ограничения

1 ≤ machines ≤ 200,000. Each time and the target are between 1 and 1,000,000,000. The answer fits signed 64-bit.

Примеры

Пример 1
Ввод:
times = [2, 3]
target = 5

Ожидаемый вывод:
expected = 6
Ввод:
std::vector<long long> times = {2, 3};
long long target = 5;

Ожидаемый вывод:
long long expected = 6;
Ввод:
long[] times = new long[] {2, 3};
long target = 5;

Ожидаемый вывод:
long expected = 6;

Пояснение

At time 6 the machines have made 3 + 2 = 5 items. At time 5 they have made only 2 + 1 = 3.

Пример 2
Ввод:
times = [4]
target = 3

Ожидаемый вывод:
expected = 12
Ввод:
std::vector<long long> times = {4};
long long target = 3;

Ожидаемый вывод:
long long expected = 12;
Ввод:
long[] times = new long[] {4};
long target = 3;

Ожидаемый вывод:
long expected = 12;

Пояснение

One machine completes its third item at 3 × 4 = 12 seconds.

Как подступиться

Сначала попробуйте сами, затем открывайте подсказки по одной.

Подсказка 1

For any chosen time, you can count how many items all machines together would finish by then.

Подсказка 2

The answer is the earliest time where that produced count reaches the target.

Подсказка 3

A monotonic condition like this is well suited to searching over time instead of simulating production.

Ожидаемая сложность

O(n log T) time, O(1) extra space

Ссылки

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