Problem:
Score : 500 points

Problem Statement

Given are N integers A_1,\ldots,A_N.

We will choose exactly K of these elements. Find the maximum possible product of the chosen elements.

Then, print the maximum product modulo (10^9+7), using an integer between 0 and 10^9+6 (inclusive).

Constraints

1 \leq K \leq N \leq 2\times 10^5

|A_i| \leq 10^9

Input

Input is given from Standard Input in the following format:

N K
A_1 \ldots A_N

Output

Print the maximum product modulo (10^9+7), using an integer between 0 and 10^9+6 (inclusive).

Sample Input 1

4 2
1 2 -3 -4

Sample Output 1

12

The possible products of the two chosen elements are 2, -3, -4, -6, -8, and 12, so the maximum product is 12.

Sample Input 2

4 3
-1 -2 -3 -4

Sample Output 2

1000000001

The possible products of the three chosen elements are -24, -12, -8, and -6, so the maximum product is -6.

We print this value modulo (10^9+7), that is, 1000000001.

Sample Input 3

2 1
-1 1000000000

Sample Output 3

1000000000

The possible products of the one chosen element are -1 and 1000000000, so the maximum product is 1000000000.

Sample Input 4

10 10
1000000000 100000000 10000000 1000000 100000 10000 1000 100 10 1

Sample Output 4

999983200

Be sure to print the product modulo (10^9+7).

Solution in C# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using static System.Math;
using static System.Console;

namespace CPLib
{
    class Atria
    {
        //いつもの
        readonly static long mod = 1000000000 + 7;
        static void Main(string[] args)
        {
            int[] nk = ReadLine().Split(' ').Select(int.Parse).ToArray();
            int n = nk[0];
            int k = nk[1];
            long[] As = ReadLine().Split(' ').Select(long.Parse).ToArray();
            //偶奇判定
            //-の数をいくつ利用してよいか
            long[] covAs = As.OrderByDescending(x => Math.Abs(x)).ToArray();
            long[] use = covAs.Where((value,index) =>index < k).ToArray();
            try
            {
                //-の数が奇数の時
                if (use.Count(x => x < 0) % 2 == 1)
                {
                    long poslong = covAs.Where((value, index) => index >= k && value > 0).ToArray()[0];
                    //これがない時、小さいものを取る条件分岐(catch)に入る

                    //一番小さい-の値をremoveして次に出現する最大の正の整数をaddする
                    for (int i = use.Length - 1; i >= 0; i--)
                    {
                        //発見
                        if (use[i] < 0)
                        {
                            use[i] = poslong;
                            break;
                        }
                    }
                }
                long ans = use[0];
                for (int i = 1; i < use.Length; i++)
                {
                    ans = modMul(ans, use[i]);
                }
                WriteLine(PosMod(ans, mod));
            }
            catch (Exception)
            {
                //小さいものを取る条件分岐
                long[] minuse = As.OrderBy(x => Math.Abs(x)).ToArray();
                long ans = minuse[0];
                for (int i = 1; i < use.Length; i++)
                {
                    ans = modMul(ans, minuse[i]);
                }
                WriteLine(PosMod(ans,mod));
            }
            
        }

        static long modMul(long a,long b)
        {
            return PosMod(a * b,mod);
        }

        /// <summary>
        /// 正剰余
        /// </summary>
        /// <param name="i"></param>
        /// <param name="j"></param>
        /// <returns></returns>
        static long PosMod(long i, long j)
        {
            return (i % j) < 0 ? (i % j) + 0 + (j < 0 ? -j : j) : (i % j + 0);
        }
    }
}