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;
typedef long long ll;
int main(){
  ll N,K;
  cin>>N>>K;
  vector<ll>X(N);
  vector<ll>date(N);
  ll num=X[0];
  ll chk=0;
  bool flag=true;
   ll min=1000000000;

 
  for(ll i=0;i<N;i++){
    cin>>X[i];
    
    if(i>=1&&X[i]>=0&&X[i-1]<0){
      num=X[i];
      chk=i;
    }
  }

  if(X[0]>=0&&num==X[0]){
    cout<<X[K-1]<<endl;
    flag=false;
  }
  
  else if(X[0]<0&&num==X[0]){
    cout<<X[N-K]<<endl;
    flag=false;
  }

  else{
    for(ll i=N-1;i>=K-1;i--){
      ll ans;
      if(i-chk+1>K){
        ans=X[i];
      }
      else{
        if(X[i]>X[i-K+1]){
          ans=X[i]+2*abs(X[i-K+1]);
          }
          else{
            ans=abs(X[i-K+1])+2*X[i];
          }
          }
      
      if(ans<min){
        min=ans;
      }
    }
  }
  
  if(flag){
  cout<<min<<endl;
  }
  
 
}