Problem p02862 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <vector>
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;
using vl = vector<ll>;
using vll = vector<vl>;
using vpll = vector<pll>;
//**関数リスト**//
int ctoi(char c) {
  switch (c) {
  case '0':
    return 0;
  case '1':
    return 1;
  case '2':
    return 2;
  case '3':
    return 3;
  case '4':
    return 4;
  case '5':
    return 5;
  case '6':
    return 6;
  case '7':
    return 7;
  case '8':
    return 8;
  case '9':
    return 9;
  default:
    return 0;
  }
}
bool pairCompare(const pll firstElof, pll secondElof) {
  return firstElof.first > secondElof.first;
}
ll nod(ll F) {
  ll keta = 1;
  while (F / 10 > 0) {
    keta++;
    F /= 10;
  }
  return keta;
}
ll gcd(ll x, ll y) {
  ll r;
  if (x < y) {
    swap(x, y);
  }
  while (y > 0) {
    r = x % y;
    x = y;
    y = r;
  }
  return x;
}
ll lcm(ll x, ll y) { return x * y / gcd(x, y); }
ll isPrime(ll x) {
  ll i;
  if (x < 2) {
    return 0;
  } else if (x == 2) {
    return 1;
  } else if (x % 2 == 0) {
    return 0;
  } else {
    for (i = 3; i * i <= x; i += 2) {
      if (x % i == 0) {
        return 0;
      }
    }
    return 1;
  }
}
void eratos(vl isPrime) {
  //(注)isPrimeのサイズはN+1にする！実際にはmain内に配置して使用
  ll i, j;
  for (i = 0; i < isPrime.size(); i++) {
    isPrime[i] = 1;
  }
  isPrime[0] = 0;
  isPrime[1] = 0;
  for (i = 2; i * i <= isPrime.size() - 1; i++) {
    if (isPrime[i] == 1) {
      j = i * 2;
      while (j <= isPrime.size() - 1) {
        isPrime[j] = 0;
        j = j + i;
      }
    }
  }
}
ll modinv(ll a, ll m) {
  ll b = m, u = 1, v = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}
ll alphabet(char C) {
  ll b = 0;
  ll key = 0;
  if (C == 'a') {
    return b;
  }
  b++;
  if (C == 'b') {
    return b;
  }
  b++;
  if (C == 'c') {
    return b;
  }
  b++;
  if (C == 'd') {
    return b;
  }
  b++;
  if (C == 'e') {
    return b;
  }
  b++;
  if (C == 'f') {
    return b;
  }
  b++;
  if (C == 'g') {
    return b;
  }
  b++;
  if (C == 'h') {
    return b;
  }
  b++;
  if (C == 'i') {
    return b;
  }
  b++;
  if (C == 'j') {
    return b;
  }
  b++;
  if (C == 'k') {
    return b;
  }
  b++;
  if (C == 'l') {
    return b;
  }
  b++;
  if (C == 'm') {
    return b;
  }
  b++;
  if (C == 'n') {
    return b;
  }
  b++;
  if (C == 'o') {
    return b;
  }
  b++;
  if (C == 'p') {
    return b;
  }
  b++;
  if (C == 'q') {
    return b;
  }
  b++;
  if (C == 'r') {
    return b;
  }
  b++;
  if (C == 's') {
    return b;
  }
  b++;
  if (C == 't') {
    return b;
  }
  b++;
  if (C == 'u') {
    return b;
  }
  b++;
  if (C == 'v') {
    return b;
  }
  b++;
  if (C == 'w') {
    return b;
  }
  b++;
  if (C == 'x') {
    return b;
  }
  b++;
  if (C == 'y') {
    return b;
  }
  b++;
  if (C == 'z') {
    return b;
  }
  return -1;
}
void bitSearch(ll n) {
  // 実際にはコピーして中身を改変して使う
  ll i, j;
  for (i = 0; i < pow(2, n); i++) {
    ll p = i;
    for (j = 0; j < n; j++) {
      cout << p % 2;
      p /= 2;
    }
    cout << endl;
  }
}
void dfsx(ll now, ll C) {
  stack<ll> S;
  S.push(now);
  // color[now] = C;
  // while (!S.empty()) {
  ll u = S.top();
  S.pop();
  // for (ll i = 0; i < road[u].size(); i++) {
  // ll v = road[u][i];
  // if (color[v] == 0) {
  // dfs(v, C);
  //}
  //}
  //}
}
void bfs(ll now) {
  // 中身は毎回書き換えて使用
  queue<ll> Q;
  Q.push(now);
  ll u;
  while (!Q.empty()) {
    u = Q.front();
    Q.pop();
    // ll v=;
    // Q.push(v);
  }
}
void dijkstra(ll s) {
  priority_queue<pll> PQ;
  // vl D(N), color(N);
  // for (i = 0; i < N; i++) {
  //	D[i] = INF;
  //	color[i] = 0;
  // }
  // D[s] = 0;
  PQ.push(make_pair(0, s));
  // color[0] = 1;
  ll q = -1;
  while (!PQ.empty()) {
    pll f = PQ.top();
    PQ.pop();
    ll u = f.second;
    // color[u] = 2;
    // if (D[u] < f.first * q) {
    //	continue;
    // }
    // for (j = 0; j < path[u].size(); j++) {
    // ll v = path[u][j].first;
    // if (color[v] == 2) {
    //	continue;
    // }
    // if (D[v] > D[u] + path[u][j].second) {
    //	D[v] = D[u] + path[u][j].second;
    //	color[v] = 1;
    //	PQ.push(make_pair(D[v] * q, v));
    // }
    //}
  }
  // cout << (D[N - 1] == INF ? -1 : D[N - 1]);
}
//**定義場所**//
ll i, j, k, l, m, n, N, M, K, H, W, L;
string S, T;
ll MOD = 1000000007;
ll ans = 1;
ll INF = 9999999999999999;
//***********//
int main() {
  ll X, Y;
  cin >> X >> Y;
  if ((X + Y) % 3 != 0) {
    cout << 0;
  } else if (X / Y > 2 || Y / X > 2) {
    cout << 0;
  } else {
    ll P = (X + Y) / 3;
    ll Q = (P - abs(X - Y)) / 2;
    P -= Q;
    vl R(340000);
    R[0] = 1;
    for (i = 1; i < 340000; i++) {
      ll z = modinv(i, MOD);
      R[i] = (R[i - 1] * (P + i)) % MOD;
      R[i] = (R[i] * z) % MOD;
    }
    cout << R[Q];
  }
}

Fixed submission:
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <vector>
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;
using vl = vector<ll>;
using vll = vector<vl>;
using vpll = vector<pll>;
//**関数リスト**//
int ctoi(char c) {
  switch (c) {
  case '0':
    return 0;
  case '1':
    return 1;
  case '2':
    return 2;
  case '3':
    return 3;
  case '4':
    return 4;
  case '5':
    return 5;
  case '6':
    return 6;
  case '7':
    return 7;
  case '8':
    return 8;
  case '9':
    return 9;
  default:
    return 0;
  }
}
bool pairCompare(const pll firstElof, pll secondElof) {
  return firstElof.first > secondElof.first;
}
ll nod(ll F) {
  ll keta = 1;
  while (F / 10 > 0) {
    keta++;
    F /= 10;
  }
  return keta;
}
ll gcd(ll x, ll y) {
  ll r;
  if (x < y) {
    swap(x, y);
  }
  while (y > 0) {
    r = x % y;
    x = y;
    y = r;
  }
  return x;
}
ll lcm(ll x, ll y) { return x * y / gcd(x, y); }
ll isPrime(ll x) {
  ll i;
  if (x < 2) {
    return 0;
  } else if (x == 2) {
    return 1;
  } else if (x % 2 == 0) {
    return 0;
  } else {
    for (i = 3; i * i <= x; i += 2) {
      if (x % i == 0) {
        return 0;
      }
    }
    return 1;
  }
}
void eratos(vl isPrime) {
  //(注)isPrimeのサイズはN+1にする！実際にはmain内に配置して使用
  ll i, j;
  for (i = 0; i < isPrime.size(); i++) {
    isPrime[i] = 1;
  }
  isPrime[0] = 0;
  isPrime[1] = 0;
  for (i = 2; i * i <= isPrime.size() - 1; i++) {
    if (isPrime[i] == 1) {
      j = i * 2;
      while (j <= isPrime.size() - 1) {
        isPrime[j] = 0;
        j = j + i;
      }
    }
  }
}
ll modinv(ll a, ll m) {
  ll b = m, u = 1, v = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}
ll alphabet(char C) {
  ll b = 0;
  ll key = 0;
  if (C == 'a') {
    return b;
  }
  b++;
  if (C == 'b') {
    return b;
  }
  b++;
  if (C == 'c') {
    return b;
  }
  b++;
  if (C == 'd') {
    return b;
  }
  b++;
  if (C == 'e') {
    return b;
  }
  b++;
  if (C == 'f') {
    return b;
  }
  b++;
  if (C == 'g') {
    return b;
  }
  b++;
  if (C == 'h') {
    return b;
  }
  b++;
  if (C == 'i') {
    return b;
  }
  b++;
  if (C == 'j') {
    return b;
  }
  b++;
  if (C == 'k') {
    return b;
  }
  b++;
  if (C == 'l') {
    return b;
  }
  b++;
  if (C == 'm') {
    return b;
  }
  b++;
  if (C == 'n') {
    return b;
  }
  b++;
  if (C == 'o') {
    return b;
  }
  b++;
  if (C == 'p') {
    return b;
  }
  b++;
  if (C == 'q') {
    return b;
  }
  b++;
  if (C == 'r') {
    return b;
  }
  b++;
  if (C == 's') {
    return b;
  }
  b++;
  if (C == 't') {
    return b;
  }
  b++;
  if (C == 'u') {
    return b;
  }
  b++;
  if (C == 'v') {
    return b;
  }
  b++;
  if (C == 'w') {
    return b;
  }
  b++;
  if (C == 'x') {
    return b;
  }
  b++;
  if (C == 'y') {
    return b;
  }
  b++;
  if (C == 'z') {
    return b;
  }
  return -1;
}
void bitSearch(ll n) {
  // 実際にはコピーして中身を改変して使う
  ll i, j;
  for (i = 0; i < pow(2, n); i++) {
    ll p = i;
    for (j = 0; j < n; j++) {
      cout << p % 2;
      p /= 2;
    }
    cout << endl;
  }
}
void dfsx(ll now, ll C) {
  stack<ll> S;
  S.push(now);
  // color[now] = C;
  // while (!S.empty()) {
  ll u = S.top();
  S.pop();
  // for (ll i = 0; i < road[u].size(); i++) {
  // ll v = road[u][i];
  // if (color[v] == 0) {
  // dfs(v, C);
  //}
  //}
  //}
}
void bfs(ll now) {
  // 中身は毎回書き換えて使用
  queue<ll> Q;
  Q.push(now);
  ll u;
  while (!Q.empty()) {
    u = Q.front();
    Q.pop();
    // ll v=;
    // Q.push(v);
  }
}
void dijkstra(ll s) {
  priority_queue<pll> PQ;
  // vl D(N), color(N);
  // for (i = 0; i < N; i++) {
  //	D[i] = INF;
  //	color[i] = 0;
  // }
  // D[s] = 0;
  PQ.push(make_pair(0, s));
  // color[0] = 1;
  ll q = -1;
  while (!PQ.empty()) {
    pll f = PQ.top();
    PQ.pop();
    ll u = f.second;
    // color[u] = 2;
    // if (D[u] < f.first * q) {
    //	continue;
    // }
    // for (j = 0; j < path[u].size(); j++) {
    // ll v = path[u][j].first;
    // if (color[v] == 2) {
    //	continue;
    // }
    // if (D[v] > D[u] + path[u][j].second) {
    //	D[v] = D[u] + path[u][j].second;
    //	color[v] = 1;
    //	PQ.push(make_pair(D[v] * q, v));
    // }
    //}
  }
  // cout << (D[N - 1] == INF ? -1 : D[N - 1]);
}
//**定義場所**//
ll i, j, k, l, m, n, N, M, K, H, W, L;
string S, T;
ll MOD = 1000000007;
ll ans = 1;
ll INF = 9999999999999999;
//***********//
int main() {
  ll X, Y;
  cin >> X >> Y;
  if ((X + Y) % 3 != 0) {
    cout << 0;
  } else if (X * 2 < Y || Y * 2 < X) {
    cout << 0;
  } else {
    ll P = (X + Y) / 3;
    ll Q = (P - abs(X - Y)) / 2;
    P -= Q;
    vl R(340000);
    R[0] = 1;
    for (i = 1; i < 340000; i++) {
      ll z = modinv(i, MOD);
      R[i] = (R[i - 1] * (P + i)) % MOD;
      R[i] = (R[i] * z) % MOD;
    }
    cout << R[Q];
  }
}