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>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

using namespace std;

typedef long long int lli;
typedef pair<int, int> ii;

template<class T>bool chmax(T &a, const T &b) { if( a < b ) { a = b; return 1; } return 0;}
template<class T>bool chmin(T &a, const T &b) { if( b < a ) { a = b; return 1; } return 0;}

#ifdef LOCAL
    #define eprintf(...) printf(__VA_ARGS__)
#else
    #define eprintf(...) 1
#endif

#define ROUNDUP(a, b)         ( ((a) + ((b) - 1) ) / (b))
#define SET_ZERO(a)             ( memset((a), 0, sizeof(a)))
#define SET_NUM_ARRAY(a,b)    ( memset((a), b, sizeof(a)))
//#define int long long int //dont forget to change int to signed

int main() {
    int N, K;
    cin >> N >> K;
    int x[100009];
    int x0;
    cin >> x0;
    x[1] = 0;
    for (int i = 2; i <= N; i++) {
        cin >> x[i];
        x[i] -= x0;
    }

    int min = 214748366;
    for (int i = 1; i <= N-K+1; i++) {
        int start = (abs(x[i] + x0) < abs(x[i + K-1] + x0))? abs(x[i] + x0) : abs(x[i+K-1] + x0);
        int cost = x[i+K-1] - x[i] + start;
        chmin<int>(min, cost);
    }
    cout << min << endl;
}