Условие
Every person shakes hands once with every other person. A handshake between A and B is the same event as one between B and A. Nobody shakes their own hand.
Implement handshake_count(people).
Input
people: The number of people.
Output
Return the total number of distinct handshakes.
Ограничения
0 ≤ people ≤ 1,000,000,000. The answer fits a signed 64-bit integer.
Примеры
Ввод:
people = 4
Ожидаемый вывод:
expected = 6Ввод:
long long people = 4;
Ожидаемый вывод:
long long expected = 6;Ввод:
long people = 4;
Ожидаемый вывод:
long expected = 6;Пояснение
The pairs are AB, AC, AD, BC, BD, and CD: six handshakes.
Ввод:
people = 1
Ожидаемый вывод:
expected = 0Ввод:
long long people = 1;
Ожидаемый вывод:
long long expected = 0;Ввод:
long people = 1;
Ожидаемый вывод:
long expected = 0;Пояснение
One person has nobody else to greet.
Как подступиться
Сначала попробуйте сами, затем открывайте подсказки по одной.
Подсказка 1
Each handshake is just an unordered pair of distinct people.
Подсказка 2
Count how many pairs can be formed from all people without double-counting.
Подсказка 3
Be careful that zero or one person means no handshakes at all.
Ожидаемая сложность
O(1) time, O(1) extra space
Ссылки
Это задание адаптировано для CodeUtility. Следуйте условию и ограничениям выше.