Problem p02585 (C++)

Buggy submission (status: Runtime Error):
#include "list"
#include <algorithm>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <unordered_set>
#include <vector>

using namespace std;
using ll = long long;
using ull = unsigned long long;
// const ll mod = 998244353;
const ll mod = 1000000007;
const int inf = 1e9;
const ll linf = 1e18;
const int DX[] = {1, -1, 0, 0};
const int DY[] = {0, 0, 1, -1};

#define rep(i, n) for (ll i = 0; i < (n); ++i)
#define rep_from(i, j, n) for (ll i = (j); i < (n); ++i)
#define rep_rev(i, n) for (ll i = n - 1; i >= 0; --i)
#define rep_from_rev(i, j, n) for (ll i = n - 1; i >= j; --i)
#define all(x) (x).begin(), (x).end()
#define sz(x) ll(x.size())

template <typename T> inline T chmax(T &a, const T b) {
  return a = (a < b) ? b : a;
}

template <typename T> inline T chmin(T &a, const T b) {
  return a = (a > b) ? b : a;
}

ll power(ll base, ll exponent) {
  if (exponent % 2) {
    return power(base, exponent - 1) * base % mod;
  } else if (exponent) {
    ll root_ans = power(base, exponent / 2);
    return root_ans * root_ans % mod;
  } else {
    return 1;
  }
}

ll inverse(ll x) { return power(x, mod - 2); }
ll gcd(ll a, ll b) {
  if (a < b)
    gcd(b, a);
  ll r;
  while (r = a % b) {
    a = b;
    b = r;
  }
  return b;
}

template <typename T> ll sum(T begin, T end) {
  return accumulate(begin, end, 0ll);
}

template <typename T> struct combination {
  vector<ll> fact, inv;

  combination(int sz) : fact(sz + 1), inv(sz + 1) {
    fact[0] = 1;
    for (int i = 1; i <= sz; i++) {
      fact[i] = fact[i - 1] * i % mod;
    }
    inv[sz] = power(fact[sz], mod - 2);
    for (int i = sz - 1; i >= 0; i--) {
      inv[i] = inv[i + 1] * (i + 1) % mod;
    }
  }

  T C(int p, int q) const {
    if (q < 0 || p < q)
      return 0;
    return T(fact[p] * inv[q] % mod * inv[p - q] % mod);
  }

  T P(int p, int q) const {
    if (p < 0 || p < q)
      return 0;
    return T(fact[p] * inv[p - q] % mod);
  }
};

using Pair = pair<int, int>;
using LPair = pair<ll, ll>;

template <ll Modulus> struct ModInt {
  ll a;

  constexpr ModInt(const ll x = 0) noexcept : a((x % mod + mod) % mod) {}

  constexpr ll &value() noexcept { return a; }

  constexpr const ll &value() const noexcept { return a; }

  constexpr ModInt operator+(const ModInt x) const noexcept {
    return ModInt(*this) += x;
  }

  constexpr ModInt operator-(const ModInt x) const noexcept {
    return ModInt(*this) -= x;
  }

  constexpr ModInt operator*(const ModInt x) const noexcept {
    return ModInt(*this) *= x;
  }

  constexpr ModInt operator/(const ModInt x) const noexcept {
    return ModInt(*this) /= x;
  }

  constexpr ModInt &operator+=(const ModInt x) noexcept {
    a += x.a;
    if (a >= Modulus) {
      a -= Modulus;
    }
    return *this;
  }

  constexpr ModInt &operator-=(const ModInt x) noexcept {
    if (a < x.a) {
      a += Modulus;
    }
    a -= x.a;
    return *this;
  }

  constexpr ModInt &operator*=(const ModInt x) noexcept {
    a = a * x.a % Modulus;
    return *this;
  }

  constexpr ModInt &operator/=(ModInt x) noexcept {
    ll exp = Modulus - 2;
    while (exp) {
      if (exp % 2) {
        *this *= x;
      }
      x *= x;
      exp /= 2;
    }
    return *this;
  }

  constexpr ModInt operator-() noexcept { return ModInt(-a); }

  friend ostream &operator<<(ostream &os, const ModInt &m) {
    os << m.a;
    return os;
  }
};

using mint = ModInt<mod>;

struct UnionFind {
  vector<int> par;
  vector<int> next;

  UnionFind(int n) : par(n, -1), next(n) { iota(all(next), 0); }

  int root(int x) {
    if (par[x] < 0)
      return x;
    return par[x] = root(par[x]);
  }

  void unite(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return;
    if (par[x] > par[y])
      swap(x, y);
    par[x] += par[y];
    par[y] = x;
    swap(next[x], next[y]);
  }

private:
  void unite_list(int x, int y) {}

  bool same(int x, int y) {
    int rx = root(x);
    int ry = root(y);
    return rx == ry;
  }
  int size(int x) { return -par[root(x)]; }
};

map<ll, int> primeFactorization(ll a) {
  map<ll, int> mp;
  for (ll i = 2; i * i <= a; i++) {
    while (a % i == 0) {
      mp[i]++;
      a /= i;
    }
  }
  if (a > 1)
    mp[a]++;
  return mp;
}

int main() {
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(15);
  ll n, k;
  cin >> n >> k;
  vector<int> p(n), c(n);
  rep(i, n) cin >> p[i];
  rep(i, n) cin >> c[i];
  rep(i, n) p[i]--;
  vector<int> used(n);
  vector<vector<int>> cyc;
  rep(i, n) {
    int x = i;
    if (used[x])
      continue;
    vector<int> a;
    while (!used[x]) {
      used[x] = 1;
      a.push_back(x);
      x = p[x];
    }
    cyc.push_back(a);
  }
  ll ans = -linf;
  for (auto v : cyc) {
    vector<ll> cum(2 * sz(v) + 1);
    rep(i, 2 * sz(v)) cum[i + 1] = cum[i] + c[v[i % sz(v)]];
    vector<ll> dp(sz(v) + 1, -linf);
    rep(i, sz(v)) rep_from(j, i, 2 * sz(v))
        chmax(dp[j - i + 1], cum[j + 1] - cum[i]);
    rep_from(i, 1, sz(v)) chmax(dp[i + 1], dp[i]);
    ll cnt = k / sz(v);
    ll loop = 0;
    for (int x : v)
      loop += c[x];
    chmax(ans, dp[min(sz(v), k)]);
    if (k > sz(v)) {
      chmax(ans, dp[min(sz(v), k)] + loop * (cnt - 1));
    }
    chmax(ans, dp[k % sz(v)] + loop * cnt);
  }
  cout << ans << endl;
}

Fixed submission:
#include "list"
#include <algorithm>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <unordered_set>
#include <vector>

using namespace std;
using ll = long long;
using ull = unsigned long long;
// const ll mod = 998244353;
const ll mod = 1000000007;
const int inf = 1e9;
const ll linf = 1e18;
const int DX[] = {1, -1, 0, 0};
const int DY[] = {0, 0, 1, -1};

#define rep(i, n) for (ll i = 0; i < (n); ++i)
#define rep_from(i, j, n) for (ll i = (j); i < (n); ++i)
#define rep_rev(i, n) for (ll i = n - 1; i >= 0; --i)
#define rep_from_rev(i, j, n) for (ll i = n - 1; i >= j; --i)
#define all(x) (x).begin(), (x).end()
#define sz(x) ll(x.size())

template <typename T> inline T chmax(T &a, const T b) {
  return a = (a < b) ? b : a;
}

template <typename T> inline T chmin(T &a, const T b) {
  return a = (a > b) ? b : a;
}

ll power(ll base, ll exponent) {
  if (exponent % 2) {
    return power(base, exponent - 1) * base % mod;
  } else if (exponent) {
    ll root_ans = power(base, exponent / 2);
    return root_ans * root_ans % mod;
  } else {
    return 1;
  }
}

ll inverse(ll x) { return power(x, mod - 2); }
ll gcd(ll a, ll b) {
  if (a < b)
    gcd(b, a);
  ll r;
  while (r = a % b) {
    a = b;
    b = r;
  }
  return b;
}

template <typename T> ll sum(T begin, T end) {
  return accumulate(begin, end, 0ll);
}

template <typename T> struct combination {
  vector<ll> fact, inv;

  combination(int sz) : fact(sz + 1), inv(sz + 1) {
    fact[0] = 1;
    for (int i = 1; i <= sz; i++) {
      fact[i] = fact[i - 1] * i % mod;
    }
    inv[sz] = power(fact[sz], mod - 2);
    for (int i = sz - 1; i >= 0; i--) {
      inv[i] = inv[i + 1] * (i + 1) % mod;
    }
  }

  T C(int p, int q) const {
    if (q < 0 || p < q)
      return 0;
    return T(fact[p] * inv[q] % mod * inv[p - q] % mod);
  }

  T P(int p, int q) const {
    if (p < 0 || p < q)
      return 0;
    return T(fact[p] * inv[p - q] % mod);
  }
};

using Pair = pair<int, int>;
using LPair = pair<ll, ll>;

template <ll Modulus> struct ModInt {
  ll a;

  constexpr ModInt(const ll x = 0) noexcept : a((x % mod + mod) % mod) {}

  constexpr ll &value() noexcept { return a; }

  constexpr const ll &value() const noexcept { return a; }

  constexpr ModInt operator+(const ModInt x) const noexcept {
    return ModInt(*this) += x;
  }

  constexpr ModInt operator-(const ModInt x) const noexcept {
    return ModInt(*this) -= x;
  }

  constexpr ModInt operator*(const ModInt x) const noexcept {
    return ModInt(*this) *= x;
  }

  constexpr ModInt operator/(const ModInt x) const noexcept {
    return ModInt(*this) /= x;
  }

  constexpr ModInt &operator+=(const ModInt x) noexcept {
    a += x.a;
    if (a >= Modulus) {
      a -= Modulus;
    }
    return *this;
  }

  constexpr ModInt &operator-=(const ModInt x) noexcept {
    if (a < x.a) {
      a += Modulus;
    }
    a -= x.a;
    return *this;
  }

  constexpr ModInt &operator*=(const ModInt x) noexcept {
    a = a * x.a % Modulus;
    return *this;
  }

  constexpr ModInt &operator/=(ModInt x) noexcept {
    ll exp = Modulus - 2;
    while (exp) {
      if (exp % 2) {
        *this *= x;
      }
      x *= x;
      exp /= 2;
    }
    return *this;
  }

  constexpr ModInt operator-() noexcept { return ModInt(-a); }

  friend ostream &operator<<(ostream &os, const ModInt &m) {
    os << m.a;
    return os;
  }
};

using mint = ModInt<mod>;

struct UnionFind {
  vector<int> par;
  vector<int> next;

  UnionFind(int n) : par(n, -1), next(n) { iota(all(next), 0); }

  int root(int x) {
    if (par[x] < 0)
      return x;
    return par[x] = root(par[x]);
  }

  void unite(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return;
    if (par[x] > par[y])
      swap(x, y);
    par[x] += par[y];
    par[y] = x;
    swap(next[x], next[y]);
  }

private:
  void unite_list(int x, int y) {}

  bool same(int x, int y) {
    int rx = root(x);
    int ry = root(y);
    return rx == ry;
  }
  int size(int x) { return -par[root(x)]; }
};

map<ll, int> primeFactorization(ll a) {
  map<ll, int> mp;
  for (ll i = 2; i * i <= a; i++) {
    while (a % i == 0) {
      mp[i]++;
      a /= i;
    }
  }
  if (a > 1)
    mp[a]++;
  return mp;
}

int main() {
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(15);
  ll n, k;
  cin >> n >> k;
  vector<int> p(n), c(n);
  rep(i, n) cin >> p[i];
  rep(i, n) cin >> c[i];
  rep(i, n) p[i]--;
  vector<int> used(n);
  vector<vector<int>> cyc;
  rep(i, n) {
    int x = i;
    if (used[x])
      continue;
    vector<int> a;
    while (!used[x]) {
      used[x] = 1;
      a.push_back(x);
      x = p[x];
    }
    cyc.push_back(a);
  }
  ll ans = -linf;
  for (auto v : cyc) {
    vector<ll> cum(2 * sz(v) + 1);
    rep(i, 2 * sz(v)) cum[i + 1] = cum[i] + c[v[i % sz(v)]];
    vector<ll> dp(2 * sz(v) + 1, -linf);
    rep(i, sz(v)) rep_from(j, i, 2 * sz(v))
        chmax(dp[j - i + 1], cum[j + 1] - cum[i]);
    rep_from(i, 1, sz(v)) chmax(dp[i + 1], dp[i]);
    ll cnt = k / sz(v);
    ll loop = 0;
    for (int x : v)
      loop += c[x];
    chmax(ans, dp[min(sz(v), k)]);
    if (k > sz(v)) {
      chmax(ans, dp[min(sz(v), k)] + loop * (cnt - 1));
    }
    chmax(ans, dp[k % sz(v)] + loop * cnt);
  }
  cout << ans << endl;
}