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;
#define rep(i, srt, end) for (long long i = (srt); i < (long long)(end); i++)

int main(){
    ll N, K;
    cin >> N >> K;
    vector<ll> x;
    ll bnd = -1;
    rep(i, 0, N){
        ll t;
        cin >> t;
        x.push_back(t);
        if(bnd == -1 && t > 0) bnd = x.size()-1;
    }

    ll ans = 1e18;
    rep(i, 0, N-K+1){
        if(i < bnd && i + K - 1 >= bnd){
            ll tmp = 2 * abs(x[i]) + x[i + K -1];
            tmp = min(tmp, abs(x[i]) + 2 * x[i + K -1]);
            ans = min(ans, tmp);
        }else if(i + K - 1 < bnd){
            ans = min(ans, abs(x[i]));
        }else{
            ans = min(ans, x[i+K-1]);
        }
    }
    cout << ans << endl;
    return 0;
}