# List of Lists LISTLIST Solution Codechef

## List of Lists LISTLIST Solution

You are given a positive integer N and an array A of size N. There are N lists L1,L2…LN. Initially, Li=[Ai].

You can perform the following operation any number of times as long as there are at least 2 lists:

• Select 2 (non-empty) lists Li and Lj (i≠j)
• Append Lj to Li and remove the list Lj. Note that this means Lj cannot be chosen in any future operation.

Find the minimum number of operations required to obtain a set of lists that satisfies the following conditions:

• The first element and last element of each list are equal.
• The first element of all the lists is the same.

Print −1 if it is not possible to achieve this via any sequence of operations.

Input Format

• The first line of input contains a single integer T, denoting the number of test cases. The description of T test cases follows.
• The first line of each test case contains an integer N.
• The second line of each test case contains N space-separated integers A1,A2,…,AN.

Output Format

For each test case, print a single line containing one integer: the minimum number of operations required to obtain an array of lists that satisfies the given conditions.

Print −1 if it is impossible to achieve such an array of lists.

Constraints

• 1≤T≤105
• 1≤N≤2⋅105
• 1≤Ai≤N
• Sum of N over all test cases doesn’t exceed 2⋅105

Sample Input 1

``````3
1
1
2
1 2
3
1 1 2``````

Sample Output 1

``````0
-1
2``````

Explanation

Test case 1: There is only one list , and it trivially satisfies the condition so no operations are required.

Test case 2: There are only 2 ways to do an operation either take list  and append it to list  or take list  and append it to list . In both cases, it is not possible to satisfy both given conditions at the same time. Hence, the answer is −1.

Test case 3: Here is one possible order of operations:

• Select the 3rd list  and append it to the 1st list .
• Then, select the 2nd list  and append it to the 1st list [1,2].

Finally, we are left with the single list [1,2,1] which satisfies the given conditions. It can be verified that it is impossible to do this using less than 2 operations.

### SOLUTION

Program Python: List of Lists LISTLIST Solution in Python

``````from collections import Counter
for _ in range(int(input())):
n = int(input())
l = list(map(int,input().split()))
c = Counter(l)
x = c.most_common(1)
#print(x)
if n == 1 or x==len(l):
print(0)
elif n>=2 and x<=1:
print(-1)
else:
print(len(l)-x+1)``````

Program C++: List of Lists LISTLIST Solution in C++

``````#include<bits/stdc++.h>
using namespace std;

int main()
{
int t;
cin>>t;
while(t--)
{
int n;
cin>>n;

int a[n];
for(int i = 0; i < n; i++)
{
cin>>a[i];
}

int mx = 1;
int c = 1;
sort(a,a+n);
for(int i = 1; i < n; i++)
{
if(a[i] == a[i-1])
{
c++;
mx = max(mx, c);
}
else{
c=1;
}
}
if(n==mx){
cout<<0<<endl;
continue;
}
if(mx==1){
cout<<-1<<endl;
continue;
}
cout<<(n-mx)+1<<endl;
}
return 0;
}``````