Problem p02616 (C++)

Buggy submission (status: Runtime Error):
// AtCoder.cpp : このファイルには 'main'
// 関数が含まれています。プログラム実行の開始と終了がそこで行われます。
//

// AtCoder.cpp : このファイルには 'main'
// 関数が含まれています。プログラム実行の開始と終了がそこで行われます。
//

#ifndef ONLINE_JUDGE

#endif
#define _USE_MATH_DEFINES
#include <math.h>

// #include<cmath>

#include <algorithm>
#include <array>
#include <assert.h>
#include <bitset>
#include <chrono>
#include <cmath>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_set>
#include <vector>
#pragma GCC optimize("Ofast")

// #include "Ants.h"
using namespace std;
typedef long long ll;
#define rad_to_deg(rad) (((rad) / 2 / M_PI) * 360)
#define EPS (1e-7)
#define INF (1e9)
#define PI (acos(-1))
#define rep(i, n) for (int i = 0; i < n; i++)
#define show(s) cout << s << endl
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define LINF (1LL << 50)
#define MOD (1e9 + 7)
#define rep1(i, n) for (int i = 1; i <= n; i++)
#define rrep(i, n) for (int i = n - 1; i >= 0; --i)

typedef pair<ll, ll> P;
ll gcd(ll a, ll b) { // 最大公約数を求める///最大公倍数a*b/gcd(a,b)
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcd(ll a, ll b) { // 最小公倍数を求める　b=0のときaを返す
  if (b == 0)
    return a;
  return (a / gcd(a, b)) * b;
}
vector<int> divnum(ll num) {
  int dig;
  vector<int> p;
  while (num) {
    dig = num % 10;
    p.push_back(dig);
    num /= 10;
  }
  return p;
}
int digiter(ll num) {
  int dig;
  vector<int> p;
  while (num) {
    dig = num % 10;
    p.push_back(dig);
    num /= 10;
  }
  return p.size();
}
vector<int> convertstring(string s) {
  vector<int> d;
  ll n = s.size();
  rep(i, n) { d.push_back(s[i] - '0'); }
  return d;
}
map<ll, int> prime_factor(ll n) {
  map<ll, int> ret;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1)
    ret[n] = 1;
  return ret;
}

vector<ll> Enumeration(ll n) {
  vector<ll> res;
  for (ll i = 1; i * i <= n; i++) {
    if (n % i != 0)
      continue;
    res.push_back(i);
    if (i * i != n)
      res.push_back(n / i);
  }

  return res;
}

ll myPow(ll x, ll n, ll m) { // x^n
  if (n == 0)
    return 1;
  if (n % 2 == 0)
    return myPow(x * x % m, n / 2, m);
  else
    return x * myPow(x, n - 1, m) % m;
}
std::vector<int> Eratosthenes(const int N) // 素数列挙
{
  std::vector<bool> is_prime(N + 1);
  for (int i = 0; i <= N; i++) {
    is_prime[i] = true;
  }
  std::vector<int> P;
  for (int i = 2; i <= N; i++) {
    if (is_prime[i]) {
      for (int j = 2 * i; j <= N; j += i) {
        is_prime[j] = false;
      }
      P.emplace_back(i);
    }
  }
  return P;
}
const ll mod = MOD;

struct mint {

  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}

  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }

  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }

  // operator long long() const { return x; }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }
struct combination { // comb(a,b)でよぶaCb

  vector<mint> fact, ifact;
  combination(ll n) : fact(n + 1), ifact(n + 1) {
    assert(n < mod);
    fact[0] = 1;
    for (ll i = 1; i <= n; ++i)
      fact[i] = fact[i - 1] * i;
    ifact[n] = fact[n].inv();
    for (ll i = n; i >= 1; --i)
      ifact[i - 1] = ifact[i] * i;
  }
  mint operator()(ll n, ll k) {
    if (k < 0 || k > n)
      return 0;
    return fact[n] * ifact[k] * ifact[n - k];
  }
} comb(1000005); // comb貯め
mint f(ll n, ll k) {
  if (n < 0)
    return 0;
  // nPk = nCk * k!
  mint res = comb(n, k);
  res *= comb.fact[k];
  return res;
}

struct SegmentTree {
private:
  int n;
  vector<int> node;

public:
  SegmentTree(vector<int> v) { // SegmentTree seg(vector<int>(N,INF))で呼び出し
    int sz = v.size();
    n = 1;
    while (n < sz)
      n *= 2;
    node.resize(2 * n - 1, INF);
    for (int i = 0; i < sz; i++)
      node[i + n - 1] = v[i];
    for (int i = n - 2; i >= 0; i--)
      node[i] = min(node[2 * i + 1], node[2 * i + 2]);
  }

  void update(int x, int val) {
    x += (n - 1);
    node[x] = val;
    while (x > 0) {
      x = (x - 1) / 2;
      node[x] = min(node[2 * x + 1], node[2 * x + 2]);
    }
  }

  int getmin(int a, int b, int k = 0, int l = 0, int r = -1) {
    if (r < 0)
      r = n;
    if (r <= a || b <= l)
      return INF;
    if (a <= l && r <= b)
      return node[k];

    int vl = getmin(a, b, 2 * k + 1, l, (l + r) / 2);
    int vr = getmin(a, b, 2 * k + 2, (l + r) / 2, r);
    return min(vl, vr);
  }
};
// 1-indexedなので注意。
struct BIT {
private:
  vector<int> bit;
  int N;

public:
  BIT(int size) {
    N = size;
    bit.resize(N + 1);
  }

  // 一点更新です
  void add(int a, int w) { // a番目をwに更新
    for (int x = a; x <= N; x += x & -x)
      bit[x] += w;
  }

  // 1~Nまでの和を求める。
  int sum(int a) {
    int ret = 0;
    for (int x = a; x > 0; x -= x & -x)
      ret += bit[x];
    return ret;
  }
};
/****Union-Ford-Tree***/
/*int par[int(0x7ffffff)];//Parent
int Rank[int(0x7ffffff)];//Deep_of_the_Tree

//int a[100] = { 4,2,3,1,5 }, m[100] ={3,2,2};
//int n = 0;
//const ll mod = 1000000007;


//n要素で初期化
void init(int n) {
        for (int i = 0; i < n; i++) {
                par[i] = i;
                Rank[i] = 0;
        }
}
//木の根探し
int find(int x) {
        if (par[x] == x) {
                return x;
        }
        else {
                return par[x] = find(par[x]);
        }
}
//xとyの属する集合を併合
void unite(int x, int y) {
        x = find(x);
        y = find(y);
        if (x == y)return;

        if (Rank[x] < Rank[y]) {
                par[x] = y;
        }
        else {
                par[y] = x;
                if (Rank[x] == Rank[y])Rank[x]++;
        }
}

bool same(int x, int y) {
        return find(x) == find(y);
}*/
// queue古い順,stack新しい順
/************************************************************************************/
int N, K;
ll A[200005];
vector<ll> p, n;
int32_t main() {
  cin >> N >> K;
  rep(i, N) {
    cin >> A[i];
    if (A[i] >= 0)
      p.push_back(A[i]);
    else {
      n.push_back(A[i]);
    }
  }
  sort(A, A + N);
  int minus = lower_bound(A, A + N, 0) - A;
  int plus = N - minus;
  int k = min(minus / 2, K / 2);
  // cout << k << endl;
  // cout << K - k * 2 << endl;
  if (K == 1) {
    cout << A[N - 1] << endl;
    return 0;
  }
  bool ok = false;
  if (p.size() > 0) {
    if (N == K)
      ok = (n.size() % 2 == 0);
    else
      ok = true;
  } else {
    ok = (K % 2 == 0);
  }
  if (ok) { // result minus;
    // cout << "work" << endl;
    mint ans = 1;
    priority_queue<P, vector<P>, greater<P>> que;
    rep(i, N) que.push(P(abs(A[i]), A[i] + mod));
    rep(i, K) {
      P p = que.top();
      que.pop();
      ans *= p.second;
    }
    // ans += mod;
    cout << ans << endl;

  } else {
    // cout << "plus" << endl;
    mint ans = 1;
    vector<ll> B;
    sort(p.begin(), p.end());
    sort(n.begin(), n.end());
    if (K % 2 != 0) {
      ans *= p.back();
      p.pop_back();
    }
    reverse(p.begin(), p.end());
    rep(i, p.size() / 2) B.push_back(p[i * 2] * p[i * 2 + 1]);
    rep(i, n.size() / 2) B.push_back(n[i * 2] * n[i * 2 + 1]);
    sort(B.rbegin(), B.rend());
    rep(i, K / 2) { ans *= B[i]; }
    ans += mod;
    cout << ans << endl;
  }
}

Fixed submission:
// AtCoder.cpp : このファイルには 'main'
// 関数が含まれています。プログラム実行の開始と終了がそこで行われます。
//

// AtCoder.cpp : このファイルには 'main'
// 関数が含まれています。プログラム実行の開始と終了がそこで行われます。
//

#ifndef ONLINE_JUDGE

#endif
#define _USE_MATH_DEFINES
#include <math.h>

// #include<cmath>

#include <algorithm>
#include <array>
#include <assert.h>
#include <bitset>
#include <chrono>
#include <cmath>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_set>
#include <vector>
#pragma GCC optimize("Ofast")

// #include "Ants.h"
using namespace std;
typedef long long ll;
#define rad_to_deg(rad) (((rad) / 2 / M_PI) * 360)
#define EPS (1e-7)
#define INF (1e9)
#define PI (acos(-1))
#define rep(i, n) for (int i = 0; i < n; i++)
#define show(s) cout << s << endl
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define LINF (1LL << 50)
#define MOD (1e9 + 7)
#define rep1(i, n) for (int i = 1; i <= n; i++)
#define rrep(i, n) for (int i = n - 1; i >= 0; --i)

typedef pair<ll, ll> P;
ll gcd(ll a, ll b) { // 最大公約数を求める///最大公倍数a*b/gcd(a,b)
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcd(ll a, ll b) { // 最小公倍数を求める　b=0のときaを返す
  if (b == 0)
    return a;
  return (a / gcd(a, b)) * b;
}
vector<int> divnum(ll num) {
  int dig;
  vector<int> p;
  while (num) {
    dig = num % 10;
    p.push_back(dig);
    num /= 10;
  }
  return p;
}
int digiter(ll num) {
  int dig;
  vector<int> p;
  while (num) {
    dig = num % 10;
    p.push_back(dig);
    num /= 10;
  }
  return p.size();
}
vector<int> convertstring(string s) {
  vector<int> d;
  ll n = s.size();
  rep(i, n) { d.push_back(s[i] - '0'); }
  return d;
}
map<ll, int> prime_factor(ll n) {
  map<ll, int> ret;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1)
    ret[n] = 1;
  return ret;
}

vector<ll> Enumeration(ll n) {
  vector<ll> res;
  for (ll i = 1; i * i <= n; i++) {
    if (n % i != 0)
      continue;
    res.push_back(i);
    if (i * i != n)
      res.push_back(n / i);
  }

  return res;
}

ll myPow(ll x, ll n, ll m) { // x^n
  if (n == 0)
    return 1;
  if (n % 2 == 0)
    return myPow(x * x % m, n / 2, m);
  else
    return x * myPow(x, n - 1, m) % m;
}
std::vector<int> Eratosthenes(const int N) // 素数列挙
{
  std::vector<bool> is_prime(N + 1);
  for (int i = 0; i <= N; i++) {
    is_prime[i] = true;
  }
  std::vector<int> P;
  for (int i = 2; i <= N; i++) {
    if (is_prime[i]) {
      for (int j = 2 * i; j <= N; j += i) {
        is_prime[j] = false;
      }
      P.emplace_back(i);
    }
  }
  return P;
}
const ll mod = MOD;

struct mint {

  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}

  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }

  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }

  // operator long long() const { return x; }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }
struct combination { // comb(a,b)でよぶaCb

  vector<mint> fact, ifact;
  combination(ll n) : fact(n + 1), ifact(n + 1) {
    assert(n < mod);
    fact[0] = 1;
    for (ll i = 1; i <= n; ++i)
      fact[i] = fact[i - 1] * i;
    ifact[n] = fact[n].inv();
    for (ll i = n; i >= 1; --i)
      ifact[i - 1] = ifact[i] * i;
  }
  mint operator()(ll n, ll k) {
    if (k < 0 || k > n)
      return 0;
    return fact[n] * ifact[k] * ifact[n - k];
  }
} comb(1000005); // comb貯め
mint f(ll n, ll k) {
  if (n < 0)
    return 0;
  // nPk = nCk * k!
  mint res = comb(n, k);
  res *= comb.fact[k];
  return res;
}

struct SegmentTree {
private:
  int n;
  vector<int> node;

public:
  SegmentTree(vector<int> v) { // SegmentTree seg(vector<int>(N,INF))で呼び出し
    int sz = v.size();
    n = 1;
    while (n < sz)
      n *= 2;
    node.resize(2 * n - 1, INF);
    for (int i = 0; i < sz; i++)
      node[i + n - 1] = v[i];
    for (int i = n - 2; i >= 0; i--)
      node[i] = min(node[2 * i + 1], node[2 * i + 2]);
  }

  void update(int x, int val) {
    x += (n - 1);
    node[x] = val;
    while (x > 0) {
      x = (x - 1) / 2;
      node[x] = min(node[2 * x + 1], node[2 * x + 2]);
    }
  }

  int getmin(int a, int b, int k = 0, int l = 0, int r = -1) {
    if (r < 0)
      r = n;
    if (r <= a || b <= l)
      return INF;
    if (a <= l && r <= b)
      return node[k];

    int vl = getmin(a, b, 2 * k + 1, l, (l + r) / 2);
    int vr = getmin(a, b, 2 * k + 2, (l + r) / 2, r);
    return min(vl, vr);
  }
};
// 1-indexedなので注意。
struct BIT {
private:
  vector<int> bit;
  int N;

public:
  BIT(int size) {
    N = size;
    bit.resize(N + 1);
  }

  // 一点更新です
  void add(int a, int w) { // a番目をwに更新
    for (int x = a; x <= N; x += x & -x)
      bit[x] += w;
  }

  // 1~Nまでの和を求める。
  int sum(int a) {
    int ret = 0;
    for (int x = a; x > 0; x -= x & -x)
      ret += bit[x];
    return ret;
  }
};
/****Union-Ford-Tree***/
/*int par[int(0x7ffffff)];//Parent
int Rank[int(0x7ffffff)];//Deep_of_the_Tree

//int a[100] = { 4,2,3,1,5 }, m[100] ={3,2,2};
//int n = 0;
//const ll mod = 1000000007;


//n要素で初期化
void init(int n) {
        for (int i = 0; i < n; i++) {
                par[i] = i;
                Rank[i] = 0;
        }
}
//木の根探し
int find(int x) {
        if (par[x] == x) {
                return x;
        }
        else {
                return par[x] = find(par[x]);
        }
}
//xとyの属する集合を併合
void unite(int x, int y) {
        x = find(x);
        y = find(y);
        if (x == y)return;

        if (Rank[x] < Rank[y]) {
                par[x] = y;
        }
        else {
                par[y] = x;
                if (Rank[x] == Rank[y])Rank[x]++;
        }
}

bool same(int x, int y) {
        return find(x) == find(y);
}*/
// queue古い順,stack新しい順
/************************************************************************************/
int N, K;
ll A[200005];
vector<ll> p, n;
int32_t main() {
  cin >> N >> K;
  rep(i, N) {
    cin >> A[i];
    if (A[i] >= 0)
      p.push_back(A[i]);
    else {
      n.push_back(A[i]);
    }
  }
  sort(A, A + N);
  int minus = lower_bound(A, A + N, 0) - A;
  int plus = N - minus;
  int k = min(minus / 2, K / 2);
  // cout << k << endl;
  // cout << K - k * 2 << endl;
  if (K == 1) {
    cout << A[N - 1] << endl;
    return 0;
  }
  bool ok = false;
  if (p.size() > 0) {
    if (N == K)
      ok = (n.size() % 2 == 0);
    else
      ok = true;
  } else {
    ok = (K % 2 == 0);
  }
  if (!ok) { // result minus;
    // cout << "work" << endl;
    mint ans = 1;
    priority_queue<P, vector<P>, greater<P>> que;
    rep(i, N) que.push(P(abs(A[i]), A[i] + mod));
    rep(i, K) {
      P p = que.top();
      que.pop();
      ans *= p.second;
    }
    // ans += mod;
    cout << ans << endl;

  } else {
    // cout << "plus" << endl;
    mint ans = 1;
    vector<ll> B;
    sort(p.begin(), p.end());
    sort(n.begin(), n.end());
    if (K % 2 != 0) {
      ans *= p.back();
      p.pop_back();
    }
    reverse(p.begin(), p.end());
    rep(i, p.size() / 2) B.push_back(p[i * 2] * p[i * 2 + 1]);
    rep(i, n.size() / 2) B.push_back(n[i * 2] * n[i * 2 + 1]);
    sort(B.rbegin(), B.rend());
    rep(i, K / 2) { ans *= B[i]; }
    ans += mod;
    cout << ans << endl;
  }
}