Problem:
Score : 600 points

Problem Statement

Snuke has an integer sequence A of length N.

He will make three cuts in A and divide it into four (non-empty) contiguous subsequences B, C, D and E.
The positions of the cuts can be freely chosen.

Let P,Q,R,S be the sums of the elements in B,C,D,E, respectively.
Snuke is happier when the absolute difference of the maximum and the minimum among P,Q,R,S is smaller.
Find the minimum possible absolute difference of the maximum and the minimum among P,Q,R,S.

Constraints

4 \leq N \leq 2 \times 10^5

1 \leq A_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Find the minimum possible absolute difference of the maximum and the minimum among P,Q,R,S.

Sample Input 1

5
3 2 4 1 2

Sample Output 1

2

If we divide A as B,C,D,E=(3),(2),(4),(1,2), then P=3,Q=2,R=4,S=1+2=3.
Here, the maximum and the minimum among P,Q,R,S are 4 and 2, with the absolute difference of 2.
We cannot make the absolute difference of the maximum and the minimum less than 2, so the answer is 2.

Sample Input 2

10
10 71 84 33 6 47 23 25 52 64

Sample Output 2

36

Sample Input 3

7
1 2 3 1000000000 4 5 6

Sample Output 3

999999994

Solution in OCaml (4.02.3) (judge verdict: Time Limit Exceeded)

open Batteries
open Printf
let () =
  let n = Scanf.scanf "%d " (fun a -> a) in
  let a_lst = Array.to_list @@ Array.init n (fun _ -> Scanf.scanf "%d " (fun a -> a)) in

  let rev_cumsum l =
    let rec aux last res = function
      | [] -> res
      | hd :: tl -> 
        let last = last + hd in
        aux last (last::res) tl
    in
    aux 0 [] l
  in

  let l = List.rev (rev_cumsum a_lst) in
  let arr = Array.of_list l in
  let n = n-1 in
  let len = Array.length arr in

  let ans = ref max_int in
  let rec loop i j k arr cnt =
    if k < n then (
      let tmp =
        List.max [arr.(i); (arr.(j)-arr.(i)); (arr.(k)-arr.(j)); (arr.(len-1)-arr.(k));] -
        List.min [arr.(i); (arr.(j)-arr.(i)); (arr.(k)-arr.(j)); (arr.(len-1)-arr.(k));] in
      if !ans < tmp then () else ans := tmp;
      loop i j (k+1) arr (cnt+1)
    ) else (
      if j < n-1 then (
        loop i (j+1) (j+2) arr cnt
      ) else (
        if i < n-1 then (
          loop (i+1) (i+2) (i+3) arr cnt
        ) else (
          ()
        )
      )
    )
  in
  loop 0 1 2 arr 0;
  printf "%d\n" !ans