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.
Vincoli
0 ≤ people ≤ 1,000,000,000. The answer fits a signed 64-bit integer.
Esempi
Input:
people = 4
Output atteso:
expected = 6Input:
long long people = 4;
Output atteso:
long long expected = 6;Input:
long people = 4;
Output atteso:
long expected = 6;Spiegazione
The pairs are AB, AC, AD, BC, BD, and CD: six handshakes.
Input:
people = 1
Output atteso:
expected = 0Input:
long long people = 1;
Output atteso:
long long expected = 0;Input:
long people = 1;
Output atteso:
long expected = 0;Spiegazione
One person has nobody else to greet.
Come affrontarlo
Prova prima da solo, poi apri un suggerimento alla volta.
Suggerimento 1
Each handshake is just an unordered pair of distinct people.
Suggerimento 2
Count how many pairs can be formed from all people without double-counting.
Suggerimento 3
Be careful that zero or one person means no handshakes at all.
Complessità attesa
O(1) time, O(1) extra space
Riferimenti
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