Second Largest Value

Problem

Return the second largest distinct value in the list. Repeated values count once.

Implement second_largest(numbers).

numbers: A list of non-negative integers.

Return the second largest distinct value, or -1 if it doesn't exist.

0 ≤ length ≤ 100,000; 0 ≤ each value ≤ 10⁹

Example 1

Input:
numbers = [4, 9, 7, 9]

Expected output:
expected = 7

Input:
std::vector<long long> numbers = {4, 9, 7, 9};

Expected output:
long long expected = 7;

Input:
long[] numbers = new long[] {4, 9, 7, 9};

Expected output:
long expected = 7;

Distinct values are 9, 7, 4; the second largest is 7.

Example 2

Input:
numbers = [5, 5]

Expected output:
expected = -1

Input:
std::vector<long long> numbers = {5, 5};

Expected output:
long long expected = -1;

Input:
long[] numbers = new long[] {5, 5};

Expected output:
long expected = -1;

Only one distinct value exists, so the answer is -1.

Try on your own first, then open one hint at a time.

Hint 1

You need the largest and the next different value, not just the top two positions.

Hint 2

Track two distinct maxima as you scan, updating them when a new value fits above or between them.

Hint 3

If no second distinct value ever appears, return the special fallback value.

Expected complexity

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

This challenge is adapted for CodeUtility. Follow the statement and constraints above.