min_instability
You are given an array a consisting of n integer numbers. Let instability of the array be the following value: max_{i = 1}^{n} a_i - min_{i = 1}^{n} a_i. You have to remove exactly one element from this array to minimize instability of the resulting (n-1)-elements array. Your task is to calculate the minimum possible instability. Input The first line of the input contains one integer n (2 ≤ n ≤ 10^5) — the number of elements in the array a. The second line of the input contains n integers a_1, a_2, ..., a_n (1 ≤ a_i ≤ 10^5) — elements of the array a. Output Print one integer — the minimum possible instability of the array if you have to remove exactly one element from the array a. Examples Input 4 1 3 3 7 Output 2 Input 2 1 100000 Output 0 Note In the first example you can remove 7 then instability of the remaining array will be 3 - 1 = 2. In the second example you can remove either 1 or 100000 then instability of the remaining array will be 100000 - 100000 = 0 and 1 - 1 = 0 correspondingly.
Function Signature
def min_instability (n : Nat) (arr : Array Nat) : Nat
Theorem Signature
def array_max (arr : Array Nat) : Nat :=
arr.foldl (fun acc x => max acc x) 0
def array_min (arr : Array Nat) : Nat :=
arr.foldl (fun acc x => min acc x) (arr[0]!)
def instability (arr : Array Nat) : Nat :=
array_max arr - array_min arr
def remove_at (arr : Array Nat) (i : Nat) : Array Nat :=
(arr.extract 0 i).append (arr.extract (i+1) arr.size)
def min_instability_prop (n : Nat) (arr : Array Nat) (out : Nat) : Prop :=
n = arr.size ∧
out = Id.run do
let mut min_inst := instability (remove_at arr 0)
for i in [1:n] do
let curr_inst := instability (remove_at arr i)
min_inst := min min_inst curr_inst
min_inst
theorem min_instability_spec (n : Nat) (arr : Array Nat) : min_instability_prop n arr (min_instability n arr)
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