Problem p02632 (C++) — buggy submission, verdict: Runtime Error

/*
これを入れて実行
g++ code.cpp
./a.out
 */

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stack>
#include <stdio.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <utility>
#include <vector>

#define all(x) (x).begin(), (x).end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

using namespace std;
typedef long long ll;
typedef long double ld;

int dy4[4] = {-1, 0, +1, 0};
int dx4[4] = {0, +1, 0, -1};
int dy8[8] = {-1, -1, 0, 1, 1, 1, 0, -1};
int dx8[8] = {0, 1, 1, 1, 0, -1, -1, -1};

const long long INF = 1LL << 60;
const ll MOD = 1e9 + 7;

bool greaterSecond(const pair<int, int> &f, const pair<int, int> &s) {
  return f.second > s.second;
}

ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}

ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

ll conbinationMemo[100][100];

void cmemoInit() {
  rep(i, 100) {
    rep(j, 100) { conbinationMemo[i][j] = -1; }
  }
}

ll nCr(ll n, ll r) {
  if (conbinationMemo[n][r] != -1)
    return conbinationMemo[n][r];
  if (r == 0 || r == n) {
    return 1;
  } else if (r == 1) {
    return n;
  }
  return conbinationMemo[n][r] = (nCr(n - 1, r) + nCr(n - 1, r - 1));
}

ll nPr(ll n, ll r) {
  r = n - r;
  ll ret = 1;
  for (ll i = n; i >= r + 1; i--)
    ret *= i;
  return ret;
}
//-----------------------ここから-----------
ll factorial[2010000];
ll invfactorial[2010000];

ll extGCD(ll a, ll b, ll &x, ll &y) {
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }

  ll d = extGCD(b, a % b, y, x);
  y -= a / b * x;
  return d;
}

ll nCrM(ll n, ll r) {
  ll ret = factorial[n];
  ret *= invfactorial[n - r];
  ret %= MOD;
  ret *= invfactorial[r];
  ret %= MOD;
  return ret;
}

ll modpow(ll a, ll b) {
  ll res = 1;
  while (b > 0) {
    if (b & 1) {
      res *= a;
      res %= MOD;
    }
    a *= a;
    a %= MOD;
    b >>= 1;
  }
  return res;
}
int main(void) {
  ll k;
  string s;
  cin >> k >> s;

  factorial[0] = 1;

  for (int i = 1; i < 2010000; i++) {
    factorial[i] = (factorial[i - 1] * i) % MOD;
  }
  for (int i = 0; i < 2010000; i++) {
    ll x, y;
    ll g = extGCD(factorial[i], MOD, x, y);
    while (x < 0)
      x += MOD;
    x %= MOD;
    invfactorial[i] = x;
  }

  ll ans = 0;
  for (ll i = 0; i <= k; i++) {
    ans += modpow(26, i) * modpow(25, k - i) % MOD *
           nCrM(s.size() + k - i - 1, s.size() - 1);
    ans %= MOD;
  }

  cout << ans << endl;
}


Error: 0

Fixed submission:

/*
これを入れて実行
g++ code.cpp
./a.out
 */

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stack>
#include <stdio.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <utility>
#include <vector>

#define all(x) (x).begin(), (x).end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

using namespace std;
typedef long long ll;
typedef long double ld;

int dy4[4] = {-1, 0, +1, 0};
int dx4[4] = {0, +1, 0, -1};
int dy8[8] = {-1, -1, 0, 1, 1, 1, 0, -1};
int dx8[8] = {0, 1, 1, 1, 0, -1, -1, -1};

const long long INF = 1LL << 60;
const ll MOD = 1e9 + 7;

bool greaterSecond(const pair<int, int> &f, const pair<int, int> &s) {
  return f.second > s.second;
}

ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}

ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

ll conbinationMemo[100][100];

void cmemoInit() {
  rep(i, 100) {
    rep(j, 100) { conbinationMemo[i][j] = -1; }
  }
}

ll nCr(ll n, ll r) {
  if (conbinationMemo[n][r] != -1)
    return conbinationMemo[n][r];
  if (r == 0 || r == n) {
    return 1;
  } else if (r == 1) {
    return n;
  }
  return conbinationMemo[n][r] = (nCr(n - 1, r) + nCr(n - 1, r - 1));
}

ll nPr(ll n, ll r) {
  r = n - r;
  ll ret = 1;
  for (ll i = n; i >= r + 1; i--)
    ret *= i;
  return ret;
}
//-----------------------ここから-----------
ll factorial[201000];
ll invfactorial[201000];

ll extGCD(ll a, ll b, ll &x, ll &y) {
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }

  ll d = extGCD(b, a % b, y, x);
  y -= a / b * x;
  return d;
}

ll nCrM(ll n, ll r) {
  ll ret = factorial[n];
  ret *= invfactorial[n - r];
  ret %= MOD;
  ret *= invfactorial[r];
  ret %= MOD;
  return ret;
}

ll modpow(ll a, ll b) {
  ll res = 1;
  while (b > 0) {
    if (b & 1) {
      res *= a;
      res %= MOD;
    }
    a *= a;
    a %= MOD;
    b >>= 1;
  }
  return res;
}
int main(void) {
  ll k;
  string s;
  cin >> k >> s;

  factorial[0] = 1;

  for (int i = 1; i < 201000; i++) {
    factorial[i] = (factorial[i - 1] * i) % MOD;
  }
  for (int i = 0; i < 201000; i++) {
    ll x, y;
    ll g = extGCD(factorial[i], MOD, x, y);
    while (x < 0)
      x += MOD;
    x %= MOD;
    invfactorial[i] = x;
  }

  ll ans = 0;
  for (ll i = 0; i <= k; i++) {
    ans += modpow(26, i) * modpow(25, k - i) % MOD *
           nCrM(s.size() + k - i - 1, s.size() - 1);
    ans %= MOD;
  }

  cout << ans << endl;
}