P1420 Longest Consecutive Sequence

Given a sequence of positive integers of length $n$, output the length of the longest consecutive sequence in the sequence. “Consecutive” means consecutive natural numbers in increasing order that appear in the sequence.

The first line contains an integer $n$. The second line contains $n$ integers $a_i$, separated by spaces.

Output one integer: the number of elements in the longest consecutive sequence.

Constraints For $100\%$ of the testdata, it is guaranteed that $1 \leq n \leq 10^4$, $1 \leq a_i \leq 10^9$. Translated by ChatGPT 5