Problem:
Score : 300 points

Problem Statement

There are N candles placed on a number line.
The i-th candle from the left is placed on coordinate x_i.
Here, x_1 < x_2 < ... < x_N holds.

Initially, no candles are burning.
Snuke decides to light K of the N candles.

Now, he is at coordinate 0.
He can move left and right along the line with speed 1.
He can also light a candle when he is at the same position as the candle, in negligible time.

Find the minimum time required to light K candles.

Constraints

1 \leq N \leq 10^5

1 \leq K \leq N

x_i is an integer.

|x_i| \leq 10^8

x_1 < x_2 < ... < x_N

Input

Input is given from Standard Input in the following format:

N K
x_1 x_2 ... x_N

Output

Print the minimum time required to light K candles.

Sample Input 1

5 3
-30 -10 10 20 50

Sample Output 1

40

He should move and light candles as follows:

Move from coordinate 0 to -10.

Light the second candle from the left.

Move from coordinate -10 to 10.

Light the third candle from the left.

Move from coordinate 10 to 20.

Light the fourth candle from the left.

Sample Input 2

3 2
10 20 30

Sample Output 2

20

Sample Input 3

1 1
0

Sample Output 3

0

There may be a candle placed at coordinate 0.

Sample Input 4

8 5
-9 -7 -4 -3 1 2 3 4

Sample Output 4

10

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
using namespace std;
using ll = long long;
int dx[] = {1,0,-1,0};
int dy[] = {0,-1,0,1};
const ll INF = 1001001001;

int main(){
    ll N,K;
    cin >> N >> K;
    vector<ll> X(N);

    ll ans = INF;
    for(ll i=0;i<N;i++) cin >> X[i];
    for(ll i=0;i<N;i++){
        if(i+K-1 >= N) continue;
        ll pre_ans;
        ll l = i,r = i+K-1;
        if(X[l]*X[r] < 0){
            pre_ans = min(abs(X[l]),abs(X[r]))*2 + max(abs(X[l]),abs(X[r]));
        }
        else{
            pre_ans = max(abs(X[l]),abs(X[r]));
        }
        ans = min(ans,pre_ans);
    }
    cout << ans << endl;

}