Подмасив

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <unordered_map>

using namespace std;


int main() {
    unordered_map<int, int> map;
    int start = 0;
    int longest = 0;

    int n, a;
    cin >> n;

    for(int i = 0; i < n; i++){
        cin >> a;
        if(map.count(a) == 0 || map[a] < start){
            map[a] = i;
            continue;
        }

        if(i - start> longest)
            longest = i - start;

        start = map[a] + 1;
        map[a] = i;
    }
    if(n - start > longest)
        longest = n - start;
    cout << longest;
    return 0;
}