B_Kalindrome_Array.cpp

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL);
#define endl '\n'
#define all(x) (x).begin(), (x).end()
#define rep(i, a, b) for (int i = a; i < b; i++)

bool solve(vector<int>& arr , int l , int r , int n) {
    while(l<=r){
        while(l<n && arr[l]==n) l++;
        while(r>=0 && arr[r]==n) r--;
        if(l<=r && arr[l]!=arr[r]) return false;
        else{
            l++;
            r--;
        }
    }
    return true;
}

int main() {
    fastio;

    int t;
    cin >> t;
    while (t--) {
        int n;
        cin>>n;
        vector<int> arr(n);
        for(int i=0;i<n;i++){
            cin>>arr[i];
        }
        int l = 0 , r = n-1;
        while(l<=n && arr[l]==arr[r]){
            l++;
            r--;
        }
        //cout<<arr[l]<<" "<<arr[r]<<endl;
        bool check = solve(arr , l , r , arr[l]);
        if(!check) check = solve(arr,l , r , arr[r]);
        if(check) cout<<"YES"<<endl;
        else cout<<"NO"<<endl;
    }

    return 0;
}