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

const int LG = 21;
const int N = 2e6 + 88;
const long long MOD = 1e9 + 7;
const long long INF = 1e9;
const long long INFLL = 1e18;

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<ll> vll;

#define forn(i, n) for (int(i) = 0; (i) != (n); (i)++)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define popcount(x) __builtin_popcount(x)
#define popcountll(x) __builtin_popcountll(x)
#define fi first
#define se second
#define re return
#define pb push_back
#define uniq(x)                                                                \\
  sort(all(x));                                                                \\
  (x).resize(unique(all(x)) - (x).begin())

#ifdef LOCAL
#define dbg(x) cerr << __LINE__ << " " << #x << " " << x << endl
#define ln cerr << __LINE__ << endl
#else
#define dbg(x) void(0)
#define ln void(0)
#endif // LOCAL

int cx[4] = {-1, 0, 1, 0};
int cy[4] = {0, -1, 0, 1};
string Yes[2] = {"No", "Yes"};
string YES[2] = {"NO", "YES"};

ll inq(ll x, ll y) {
  if (!y)
    re 1 % MOD;
  ll l = inq(x, y / 2);
  if (y % 2)
    re l *l % MOD *x % MOD;
  re l *l % MOD;
}

ll rev(ll x) { return inq(x, MOD - 2); }

bool __precomputed_combinatorics = 0;
vector<ll> __fact, __ufact, __rev;

void __precompute_combinatorics() {
  __precomputed_combinatorics = 1;
  __fact.resize(N);
  __ufact.resize(N);
  __rev.resize(N);
  __rev[1] = 1;
  for (int i = 2; i < N; i++)
    __rev[i] = MOD - __rev[MOD % i] * (MOD / i) % MOD;
  __fact[0] = 1, __ufact[0] = 1;
  for (int i = 1; i < N; i++)
    __fact[i] = __fact[i - 1] * i % MOD,
    __ufact[i] = __ufact[i - 1] * __rev[i] % MOD;
}

ll fact(int x) {
  if (!__precomputed_combinatorics)
    __precompute_combinatorics();
  return __fact[x];
}

ll cnk(int n, int k) {
  if (k < 0 || k > n)
    return 0;
  if (!__precomputed_combinatorics)
    __precompute_combinatorics();
  return __fact[n] * __ufact[n - k] % MOD * __ufact[k] % MOD;
}

int Root(int x, vector<int> &root) {
  if (x == root[x])
    return x;
  return root[x] = Root(root[x], root);
}

void Merge(int v, int u, vector<int> &root, vector<int> &sz) {
  v = Root(v, root), u = Root(u, root);
  if (v == u)
    return;
  if (sz[v] < sz[u]) {
    sz[u] += sz[v];
    root[v] = u;
  } else {
    sz[v] += sz[u];
    root[u] = v;
  }
}

int ok(int x, int n) { return 0 <= x && x < n; }

void bfs(int v, vi &dist, vector<vi> &graph) {
  fill(all(dist), -1);
  dist[v] = 0;
  vi q = {v};
  for (int i = 0; i < q.size(); i++) {
    for (auto u : graph[q[i]]) {
      if (dist[u] == -1) {
        dist[u] = dist[q[i]] + 1;
        q.push_back(u);
      }
    }
  }
}

vector<int> z_func(string &s) {
  vector<int> z(s.size());
  z[0] = s.size();
  int L = 0, R = 0;
  for (int i = 1; i < s.size(); i++) {
    z[i] = max(0, min(z[i - L], R - i));
    while (i + z[i] < s.size() && s[i + z[i]] == s[z[i]])
      z[i]++;
    if (i + z[i] > R) {
      R = i + z[i];
      L = i;
    }
  }
  return z;
}

vector<int> p_func(string &s) {
  vector<int> p(s.size());
  for (int i = 1; i < s.size(); i++) {
    int j = p[i - 1];
    while (j > 0 && s[i] != s[j])
      j = p[j - 1];
    if (s[i] == s[j])
      j++;
    p[i] = j;
  }
  return p;
}

vector<int> d1_func(string &s) {
  vector<int> d1(s.size());
  int L = 0, R = -1;
  for (int i = 0; i < s.size(); i++) {
    int k = 0;
    if (i <= R)
      k = min(R - i + 1, d1[R - i + L]);
    while (i + k < s.size() && i - k >= 0 && s[i - k] == s[i + k])
      k++;
    d1[i] = k--;
    if (i + k > R) {
      L = i - k;
      R = i + k;
    }
  }
  return d1;
}

vector<int> d2_func(string &s) {
  vector<int> d2(s.size());
  int L = 0, R = -1;
  for (int i = 1; i < s.size(); i++) {
    int k = 0;
    if (i <= R)
      k = min(R - i + 1, d2[R - i + L + 1]);
    while (i + k < s.size() && i - k - 1 >= 0 && s[i - k - 1] == s[i + k])
      k++;
    d2[i] = k--;
    if (i + k > R) {
      L = i - k - 1;
      R = i + k;
    }
  }
  return d2;
}

ll log10(ll x) {
  if (x < 10)
    re 1;
  re 1 + log10(x / 10);
}

ll ds(ll x) {
  if (x < 10)
    return x;
  re x % 10 + ds(x / 10);
}

double sqr(double x) { return x * x; }

bool in(int bit, int mask) { return (mask & (1 << bit)) > 0; }

void Del(vector<int> &v, int pos) {
  swap(v[pos], v[v.size() - 1]);
  v.pop_back();
}

long long g(vector<long long> &p, int pos) {
  if (ok(pos, p.size()))
    return p[pos];
  if (pos < 0 || p.size() == 0)
    return 0;
  return p.back();
}

int g(vector<int> &p, int pos) {
  if (ok(pos, p.size()))
    return p[pos];
  if (pos < 0 || p.size() == 0)
    return 0;
  return p.back();
}

signed main() {
  srand(time(NULL));
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ll n, k;
  cin >> k;
  string s;
  cin >> s;
  n = s.size();
  ll ans = 0;
  for (int c = n; c <= n + k; c++)
    ans += inq(25, n + k - c) * cnk(n + k, c) % MOD;
  cout << ans % MOD;
}

/* Note:
Check constants at the beginning of the code.
    N is set to 4e5 but be careful in problems with large constant factor.
    Setting N in every problem is more effective.
Check corner cases.
    N = 1
No def int long long for now.
Add something here.
*/


Error: WA

Fixed submission:

const int LG = 21;
const int N = 1e6 + 88;
const long long MOD = 1e9 + 7;
const long long INF = 1e9;
const long long INFLL = 1e18;

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<ll> vll;

#define forn(i, n) for (int(i) = 0; (i) != (n); (i)++)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define popcount(x) __builtin_popcount(x)
#define popcountll(x) __builtin_popcountll(x)
#define fi first
#define se second
#define re return
#define pb push_back
#define uniq(x)                                                                \\
  sort(all(x));                                                                \\
  (x).resize(unique(all(x)) - (x).begin())

#ifdef LOCAL
#define dbg(x) cerr << __LINE__ << " " << #x << " " << x << endl
#define ln cerr << __LINE__ << endl
#else
#define dbg(x) void(0)
#define ln void(0)
#endif // LOCAL

int cx[4] = {-1, 0, 1, 0};
int cy[4] = {0, -1, 0, 1};
string Yes[2] = {"No", "Yes"};
string YES[2] = {"NO", "YES"};

ll inq(ll x, ll y) {
  if (!y)
    re 1 % MOD;
  ll l = inq(x, y / 2);
  if (y % 2)
    re l *l % MOD *x % MOD;
  re l *l % MOD;
}

ll rev(ll x) { return inq(x, MOD - 2); }

bool __precomputed_combinatorics = 0;
vector<ll> __fact, __ufact, __rev;

void __precompute_combinatorics() {
  __precomputed_combinatorics = 1;
  __fact.resize(N);
  __ufact.resize(N);
  __rev.resize(N);
  __rev[1] = 1;
  for (int i = 2; i < N; i++)
    __rev[i] = MOD - __rev[MOD % i] * (MOD / i) % MOD;
  __fact[0] = 1, __ufact[0] = 1;
  for (int i = 1; i < N; i++)
    __fact[i] = __fact[i - 1] * i % MOD,
    __ufact[i] = __ufact[i - 1] * __rev[i] % MOD;
}

ll fact(int x) {
  if (!__precomputed_combinatorics)
    __precompute_combinatorics();
  return __fact[x];
}

ll cnk(int n, int k) {
  if (k < 0 || k > n)
    return 0;
  if (!__precomputed_combinatorics)
    __precompute_combinatorics();
  return __fact[n] * __ufact[n - k] % MOD * __ufact[k] % MOD;
}

int Root(int x, vector<int> &root) {
  if (x == root[x])
    return x;
  return root[x] = Root(root[x], root);
}

void Merge(int v, int u, vector<int> &root, vector<int> &sz) {
  v = Root(v, root), u = Root(u, root);
  if (v == u)
    return;
  if (sz[v] < sz[u]) {
    sz[u] += sz[v];
    root[v] = u;
  } else {
    sz[v] += sz[u];
    root[u] = v;
  }
}

int ok(int x, int n) { return 0 <= x && x < n; }

void bfs(int v, vi &dist, vector<vi> &graph) {
  fill(all(dist), -1);
  dist[v] = 0;
  vi q = {v};
  for (int i = 0; i < q.size(); i++) {
    for (auto u : graph[q[i]]) {
      if (dist[u] == -1) {
        dist[u] = dist[q[i]] + 1;
        q.push_back(u);
      }
    }
  }
}

vector<int> z_func(string &s) {
  vector<int> z(s.size());
  z[0] = s.size();
  int L = 0, R = 0;
  for (int i = 1; i < s.size(); i++) {
    z[i] = max(0, min(z[i - L], R - i));
    while (i + z[i] < s.size() && s[i + z[i]] == s[z[i]])
      z[i]++;
    if (i + z[i] > R) {
      R = i + z[i];
      L = i;
    }
  }
  return z;
}

vector<int> p_func(string &s) {
  vector<int> p(s.size());
  for (int i = 1; i < s.size(); i++) {
    int j = p[i - 1];
    while (j > 0 && s[i] != s[j])
      j = p[j - 1];
    if (s[i] == s[j])
      j++;
    p[i] = j;
  }
  return p;
}

vector<int> d1_func(string &s) {
  vector<int> d1(s.size());
  int L = 0, R = -1;
  for (int i = 0; i < s.size(); i++) {
    int k = 0;
    if (i <= R)
      k = min(R - i + 1, d1[R - i + L]);
    while (i + k < s.size() && i - k >= 0 && s[i - k] == s[i + k])
      k++;
    d1[i] = k--;
    if (i + k > R) {
      L = i - k;
      R = i + k;
    }
  }
  return d1;
}

vector<int> d2_func(string &s) {
  vector<int> d2(s.size());
  int L = 0, R = -1;
  for (int i = 1; i < s.size(); i++) {
    int k = 0;
    if (i <= R)
      k = min(R - i + 1, d2[R - i + L + 1]);
    while (i + k < s.size() && i - k - 1 >= 0 && s[i - k - 1] == s[i + k])
      k++;
    d2[i] = k--;
    if (i + k > R) {
      L = i - k - 1;
      R = i + k;
    }
  }
  return d2;
}

ll log10(ll x) {
  if (x < 10)
    re 1;
  re 1 + log10(x / 10);
}

ll ds(ll x) {
  if (x < 10)
    return x;
  re x % 10 + ds(x / 10);
}

double sqr(double x) { return x * x; }

bool in(int bit, int mask) { return (mask & (1 << bit)) > 0; }

void Del(vector<int> &v, int pos) {
  swap(v[pos], v[v.size() - 1]);
  v.pop_back();
}

long long g(vector<long long> &p, int pos) {
  if (ok(pos, p.size()))
    return p[pos];
  if (pos < 0 || p.size() == 0)
    return 0;
  return p.back();
}

int g(vector<int> &p, int pos) {
  if (ok(pos, p.size()))
    return p[pos];
  if (pos < 0 || p.size() == 0)
    return 0;
  return p.back();
}

signed main() {
  srand(time(NULL));
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ll n, k;
  cin >> k;
  string s;
  cin >> s;
  n = s.size();
  ll ans = 0;
  for (int c = n; c <= n + k; c++)
    ans += inq(25, n + k - c) * cnk(n + k, c) % MOD;
  cout << ans % MOD;
}

/* Note:
Check constants at the beginning of the code.
    N is set to 4e5 but be careful in problems with large constant factor.
    Setting N in every problem is more effective.
Check corner cases.
    N = 1
No def int long long for now.
Add something here.
*/