codeforces#P1805F1. Survival of the Weakest (easy version)
Survival of the Weakest (easy version)
Description
This is the easy version of the problem. It differs from the hard one only in constraints on $n$. You can make hacks only if you lock both versions.
Let $a_1, a_2, \ldots, a_n$ be an array of non-negative integers. Let $F(a_1, a_2, \ldots, a_n)$ be the sorted in the non-decreasing order array of $n - 1$ smallest numbers of the form $a_i + a_j$, where $1 \le i < j \le n$. In other words, $F(a_1, a_2, \ldots, a_n)$ is the sorted in the non-decreasing order array of $n - 1$ smallest sums of all possible pairs of elements of the array $a_1, a_2, \ldots, a_n$. For example, $F(1, 2, 5, 7) = [1 + 2, 1 + 5, 2 + 5] = [3, 6, 7]$.
You are given an array of non-negative integers $a_1, a_2, \ldots, a_n$. Determine the single element of the array $\underbrace{F(F(F\ldots F}_{n-1}(a_1, a_2, \ldots, a_n)\ldots))$. Since the answer can be quite large, output it modulo $10^9+7$.
The first line contains one integer $n$ ($2 \le n \le 3000$) — the initial length of the array.
The second line contains $n$ integers $a_1, a_2, \ldots, a_n$ ($0 \le a_i \le 10^9$) — the array elements.
Output a single number — the answer modulo $10^9 + 7$.
Input
The first line contains one integer $n$ ($2 \le n \le 3000$) — the initial length of the array.
The second line contains $n$ integers $a_1, a_2, \ldots, a_n$ ($0 \le a_i \le 10^9$) — the array elements.
Output
Output a single number — the answer modulo $10^9 + 7$.
5
1 2 4 5 6
9
1 1 1 7 7 7 9 9 9
7
1 7 9 2 0 0 9
3
1000000000 1000000000 777
34
256
20
1540
Note
In the first test, the array is transformed as follows: $[1, 2, 4, 5, 6] \to [3, 5, 6, 6] \to [8, 9, 9] \to [17, 17] \to [34]$. The only element of the final array is $34$.
In the second test, $F(a_1, a_2, \ldots, a_n)$ is $[2, 2, 2, 8, 8, 8, 8, 8]$. This array is made up of $3$ numbers of the form $1 + 1$ and $5$ numbers of the form $1 + 7$.
In the fourth test, the array is transformed as follows: $[10^9, 10^9, 777] \to [10^9+777, 10^9+777] \to [2 \cdot 10^9 + 1554]$. $2 \cdot 10^9 + 1554$ modulo $10^9+7$ equals $1540$.