Problema
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.
Restricciones
0 ≤ people ≤ 1,000,000,000. The answer fits a signed 64-bit integer.
Ejemplos
Entrada:
people = 4
Salida esperada:
expected = 6Entrada:
long long people = 4;
Salida esperada:
long long expected = 6;Entrada:
long people = 4;
Salida esperada:
long expected = 6;Explicación
The pairs are AB, AC, AD, BC, BD, and CD: six handshakes.
Entrada:
people = 1
Salida esperada:
expected = 0Entrada:
long long people = 1;
Salida esperada:
long long expected = 0;Entrada:
long people = 1;
Salida esperada:
long expected = 0;Explicación
One person has nobody else to greet.
Cómo abordarlo
Inténtalo primero por tu cuenta y luego abre las pistas una a una.
Pista 1
Each handshake is just an unordered pair of distinct people.
Pista 2
Count how many pairs can be formed from all people without double-counting.
Pista 3
Be careful that zero or one person means no handshakes at all.
Complejidad esperada
O(1) time, O(1) extra space
Referencias
Este reto está adaptado para CodeUtility. Sigue el enunciado y las restricciones indicadas arriba.