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>
#define ll long long
#define pb push_back
using namespace std;
vector<ll>v;
int main()
{
    int n, k;
    cin>>n>>k;
    int pos=0, t=0;
    for(int i=0;i<n; i++)
    {
        ll x;
        cin>>x;
        if(x<0) v.pb(x);
        else
        {
            if(t==0 && x)
            {
                v.pb(0);
                t=1;
            }
            v.pb(x);
            t=1;
            if(x==0) k--;
        }
    }
    ll ans=100000000000000000;
    //for(auto it:v) cout<<it<<" ";
    //cout<<endl;
    int sz=v.size();
    for(int i=0; i<=k; i++)
    {
        if(pos-i>=0 && pos-i+k<sz)
            ans=min(ans, abs(v[pos]-v[pos-i])+abs(v[pos-i]-v[pos-i+k]));
        //cout<<ans<<endl;
    }
    for(int i=0; i<=k; i++)
    {
        if(pos+i<sz && pos+i-k>=0)
            ans=min(ans, abs(v[pos]-v[pos+i])+abs(v[pos+i]-v[pos+i-k]));
    }
    cout<<ans<<endl;
    return 0;
}