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;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15); 
    int n, m;
    cin >> n >> m;
    vector<int> a(n);
    for (int i = 0; i < n; ++i) {
        cin >> a[i]; 
    }
    int mk = 0; 
    for (int i = 0; i < n; ++i) {
        if (a[i] >= 0) {
            mk = i; 
            break; 
        } 
    }
    vector<int> pre(n, 0);
    vector<int> suf(n, 0);
    for (int i = mk; i < n; ++i) {
        suf[i - mk + 1] = a[i]; 
    } 
    for (int i = mk - 1; i >= 0; --i) {
        pre[mk - i] = -a[i]; 
    }
/*
    for (int i = 1; i <= n - mk; ++i) {
        cerr << suf[i] << " "; 
    }   cerr << endl; 
    for (int i = 1; i <= mk; ++i) {
        cerr << pre[i] << " "; 
    }   cerr << endl; 
*/
    int ans = INT_MAX; 
    for (int i = 1; i <= min(n - mk, m); ++i) {
        ans = min(ans, 2 * suf[i] + pre[m - i]); 
    }
    for (int i = 1; i <= min(mk, m); ++i) {
        ans = min(ans, 2 * pre[i] + suf[m - i]); 
    }
    cout << ans << endl; 
    return 0; 
}