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: Wrong Answer)

#include<bits/stdc++.h>
using namespace std;
const long long INFdesu=2E10;


int main(){
    int N,K;
    long long X[100010];
    cin >> N >> K;
    long long minV=INFdesu;
    int left=0;
    int i;
    for(i=0;i<N;i++) {
        cin >> X[i];
        if (X[i]<0) left=i+1;
    }

    
    //最初左にi個行く
    for(i=1;i<=left && i<K && K-i<=N-left;i++){
        minV=min(minV,-2*X[left-i]+X[K-i+left-1]);
    }

    //最初右にi個行く
    for(i=1;i<=N-left && i<K && K-i<=left;i++){
        minV=min(minV,2*X[left+i-1]-X[left-K+i]);
    }

    if(left>=K && X[left]==0 && left<N) minV=min(minV,-X[left-K+1]);
    if(left>=K && (X[left]!=0 || left>=N)) minV=min(minV,-X[left-K]);
    if(N-left>=K) minV=min(minV,X[left+K-1]);
    cout << minV << endl;
}