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;
vector<int>v;
vector<int>s;
int main(){
	int n,k;
	int x[100000];
	cin>>n>>k;
	for(int i=0;i<n;i++)cin>>x[i];
	for(int i=n-1;i>=0;i--){
		if(x[i]<=0)v.push_back(x[i]);
		else s.push_back(x[i]);
	}
	if(s.size()==0){
		cout<<abs(v[k-1])<<endl;
		return 0;
	}
	reverse(s.begin(),s.end());
	
	if(v.size()==0){
		cout<<s[k-1]<<endl;
		return 0;
	}
	if(k==1){
		cout<<min(abs(v[0]),s[0])<<endl;
		return 0;
	}
  int ans=1000000000;
  if(s.size()>=k)ans=s[k-1];
	for(int i=0;i<v.size();i++){
		if(i==k)break;
		if(i==k-1)ans=min(ans,abs(v[i]*2));
		else if(k-i-2<s.size())ans=min(ans,abs(v[i])+s[k-i-2]);
		else break;
	}
	cout<<ans<<endl;
	return 0;
}