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 Python (3.8.2) (judge verdict: Wrong Answer)

#!/usr/bin/env python3
#
# Author: Tetsuya Ishikawa <tiskw111@gmail.com>
# Date  : July 05, 2020
##################################################### SOURCE START #####################################################

import heapq
import collections

class HeapQueue:

    def __init__(self, xs, mode):
        if   mode == "min": self.xs = [+x for x in xs]
        elif mode == "max": self.xs = [-x for x in xs]
        else              : raise NotImplementedError("HeapQueue.__init__: mode should be 'min' or 'max'")
        heapq.heapify(xs)
        self.mode = mode

    def __len__(self):
        return len(self.xs)

    def pop(self):
        if   self.mode == "min": return heapq.heappop(self.xs)
        elif self.mode == "max": return heapq.heappop(self.xs) * (-1)

    def push(self, x):
        if   self.mode == "min": return heapq.heappush(self.xs,  x)
        elif self.mode == "max": return heapq.heappush(self.xs, -x)

    # @staticmethod
    # def __test01__():
    #     xs = HeapQueue([-3, 2, 9, -4], "min")
    #     x0 = xs.pop()
    #     x1 = xs.pop()
    #     x2 = xs.pop()
    #     x3 = xs.pop()
    #     return (x0 == -4 and x1 == -3 and x2 == 2 and x3 == 9)


N, K = tuple(map(int, input().strip().split()))
As = list(map(int, input().strip().split()))

D = int(1E9 + 7)
r = 1

if N == K:

    for a in As:
        r = (r * a) % D
    print(r)
    exit()

if all(a >= 0 for a in As):

    As = sorted(As, reverse=True)
    for a in As[:K]:
        r = (r * a) % D
    print(r)
    exit()

if K % 2 == 1 and all(a < 0 for a in As):

    As = sorted(As, reverse=True)
    for a in As[:K]:
        r = (r * a) % D
    print(r)
    exit()

if K % 2 == 0 and all(a < 0 for a in As):

    As = sorted(As)
    for a in As[:K]:
        r = (r * a) % D
    print(r)
    exit()

else:

    As = sorted(As, key = lambda a: abs(a), reverse=True)

    used = As[:K]
    rest = As[K:]
    num_negative_sign = sum([1 if x < 0 else 0 for x in used])

    if num_negative_sign % 2 != 0:

        used_min_pos = None
        used_min_neg = None
        for k in range(K-1, -1, -1):
            if   used_min_pos is None and used[k] >= 0: used_min_pos = k
            elif used_min_neg is None and used[k] <  0: used_min_neg = k
            if used_min_pos and used_min_neg:
                break

        rest_min_pos = None
        rest_min_neg = None
        for k in range(N-K-1, -1, -1):
            if   rest_min_pos is None and rest[k] >= 0: rest_min_pos = k
            elif rest_min_neg is None and rest[k] <  0: rest_min_neg = k
            if rest_min_pos and rest_min_neg:
                break

        if used_min_pos is None or rest_min_neg is None:
            used[used_min_neg] = rest_min_pos
        elif used_min_neg is None or rest_min_pos is None:
            used[used_min_pos] = rest_min_neg
        else:
            v1 = abs(used[used_min_pos] * rest[rest_min_neg])
            v2 = abs(used[used_min_neg] * rest[rest_min_pos])
            if v1 < v2:
                used[used_min_pos] = rest_min_neg
            else:
                used[used_min_neg] = rest_min_pos

    for a in used:
        r = (r * a) % D
    print(r)
    exit()


##################################################### SOURCE FINISH ####################################################
# vim: expandtab tabstop=4 shiftwidth=4 fdm=marker