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 rep(i,n) for(long long int i = 0; i < n; i++)
#define _rep(i,m,n) for(long long int i = m; i < n; i++)
#define print(n) std::cout << n << std::endl
#define _print(n) std::cout << n
using namespace std;
typedef long long ll;
const int N = 1000000;
const ll mod = 1000000007;
using Graph = vector<vector<int>>;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll gcd(ll a, ll b){
   if(b == 0) return a;
   return gcd(b, a % b);
}
int main(){
   int n,k; cin >> n >> k;
   vector<int> x(n);
   rep(i,n) cin >> x[i];
   
   int MIN = INFINITY;
   if(k == 1){
      cout << abs(x[0]) << endl;
      return 0;
   }
   if(n == k){
      if(x[n - 1] <= 0) cout << abs(x[0]) << endl;
      else if(x[0] >= 0) cout << x[n - 1] << endl;
      else{
      if(abs(x[0]) >= x[n - 1])cout << abs(x[0]) + 2 * x[n - 1] << endl;
      else cout << abs(x[0] * 2) + x[n - 1]  << endl;
      return 0;
      }
   }
   rep(i,n - k){
      if(x[i + (k - 1)] <= 0)MIN = min(abs(x[i]), MIN);
      else if(x[i] >= 0)MIN = min(x[i + (k - 1)], MIN);
      else{ 
         if(abs(x[i]) >= x[i + (k - 1)])MIN = min(abs(x[i]) + 2 * x[i + (k - 1)], MIN);
         else MIN = min(abs(x[i] * 2) + x[i + (k - 1)], MIN);
      }
   }
   cout << MIN << endl;
}