Problema
Return the second largest distinct value in the list. Repeated values count once.
Implement second_largest(numbers).
Input
numbers: A list of non-negative integers.
Output
Return the second largest distinct value, or -1 if it doesn't exist.
Vincoli
0 ≤ length ≤ 100,000; 0 ≤ each value ≤ 10⁹
Esempi
Input:
numbers = [4, 9, 7, 9]
Output atteso:
expected = 7Input:
std::vector<long long> numbers = {4, 9, 7, 9};
Output atteso:
long long expected = 7;Input:
long[] numbers = new long[] {4, 9, 7, 9};
Output atteso:
long expected = 7;Spiegazione
Distinct values are 9, 7, 4; the second largest is 7.
Input:
numbers = [5, 5]
Output atteso:
expected = -1Input:
std::vector<long long> numbers = {5, 5};
Output atteso:
long long expected = -1;Input:
long[] numbers = new long[] {5, 5};
Output atteso:
long expected = -1;Spiegazione
Only one distinct value exists, so the answer is -1.
Come affrontarlo
Prova prima da solo, poi apri un suggerimento alla volta.
Suggerimento 1
You need the largest and the next different value, not just the top two positions.
Suggerimento 2
Track two distinct maxima as you scan, updating them when a new value fits above or between them.
Suggerimento 3
If no second distinct value ever appears, return the special fallback value.
Complessità attesa
O(n) time, O(1) extra space
Riferimenti
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