Problem C
Exactly Paired
Zapray recently did not have much time to finish his homework due to his addiction to Pokemon. What is even worse, this week’s algorithm class has assigned a very challenging homework problem: “Given an array of integers, find the longest consecutive sub-array so that each element in the sub-array appears exactly twice.”
Zapray remembers how to find the longest consecutive sub-array so that each element in the sub-array appears exactly once using sliding window. But he could not figure out how to extend it for this problem. Could you help Zapray?
Input
The first line of the input has an integer $N$ ($1 \leq N \leq 10^5$), the length of the array. The second line contains $N$ positive integers giving the elements of the array. Each integer is no larger than $10^5$.
Output
Output the length of the longest sub-array so that each element in the sub-array appears exactly twice.
| Sample Input 1 | Sample Output 1 |
|---|---|
6 1 2 3 3 4 2 |
2 |
| Sample Input 2 | Sample Output 2 |
|---|---|
8 1 2 1 3 1 3 1 2 |
4 |
| Sample Input 3 | Sample Output 3 |
|---|---|
7 1 10 100 1000 100 10 1 |
0 |
