Don't know what's wrong with this solution of Concussive Sequence

help
1

Tried several times, But don’t why it is not passing even subtask 1

#include<bits/stdc++.h>

using namespace std;

void print(vector<int> &ans){
    int i,n= ans.size();
    for(i= 0;i<n;i++)
        cout<<ans[i]<<" ";
    cout<<endl;
}

bool isValid(vector<int> &ans){
    int i,n= ans.size();
    for(i= 1;i<n-1;i++){
        if(ans[i-1]>ans[i] && ans[i]<ans[i+1]) continue;
        if(ans[i-1]<ans[i] && ans[i]>ans[i+1]) continue;
        return false;
    }
    return true;
}

void solve(){
    int n,i;
    cin>>n;
    vector<int> arr(n);
    for(i= 0;i<n;i++)
        cin>>arr[i];
    sort(arr.begin(), arr.end());
    vector<int> ans1(n), ans2(n);
    int k;
    k= n-1;
    for(i= 0;k>=0 && i<n;i+= 2)
        ans2[i]= arr[k--];
    for(i= 1;k>=0 && i<n;i+= 2)
        ans2[i]= arr[k--];
        
    k= 0;
    for(i= 0;k<n && i<n;i+=2)
        ans1[i]= arr[k++];
    for(i= 1;k<n && i<n;i+=2)
        ans1[i]= arr[k++];
    bool flag2= isValid(ans2), flag1= isValid(ans1);
    // cout<<flag1<<" "<<flag2<<endl;
    if(flag1== false && flag2== false){
        cout<<-1<<endl;
        return;
    }
    if(flag2== true){
        print(ans2);
        return;
    }
    print(ans1);
}

int main(){
    int t;
    cin>>t;
    while(t--)
        solve();
}