Problem p02572 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cassert>
#include <cmath>
#include <functional>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stack>
#include <stdio.h>
#include <string>
#include <tuple>
#include <vector>
// #include<bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define rep(i, x) for (ll i = 0; i < x; i++)
#define rep2(i, x) for (ll i = 1; i <= x; i++)
#define all(a) (a).begin(), (a).end()
using ll = long long;
using ld = long double;
using namespace std;
const ll INF = 1000000000000000000;
const ll mod = 1000000007;
const ld pi = 3.141592653589793238;

/*bool IsPrime(ll num) {
        if (num < 2) return false;
        else if (num == 2) return true;
        else if (num % 2 == 0) return false; // 偶数はあらかじめ除く
        double sqrtNum = sqrt(num);
        for (int i = 3; i <= sqrtNum; i += 2) {
                if (num % i == 0) { // 素数ではない
                        return false;
                }
        }
        // 素数である
        return true;
}*/
/*ll gcd(ll a, ll b) {
        if (a < b)swap(a, b);
        if (a % b == 0)return b;
        return gcd(b, a % b);
}
ll lcm(ll a, ll b) {
        return a / gcd(a, b) * b;
}*/
/*ll keta(ll n) {
        ll res = 0;
        while (n >= 1) {
                res += n % 10; n /= 10;
        }
        return res;
}*/
/*ll modpow(ll x, ll y, ll mod) {
        ll res = 1;
        while (y) {
                if (y % 2) { res *= x; res %= mod; }
                x = x * x % mod; y /= 2;
        }
        return res;
}*/
/*ll nCk(ll n, ll k) {
        ll a = 1, b = 1;
        for (int h = n - k + 1; h <= n; h++) { a *= h; a %= mod; }
        for (int h = 1; h <= k; h++) { b *= h; b %= mod; }
        return a * modpow(b, mod - 2) % mod;
}*/
// printf("%.10f\n", n);

ll test[123456], rui[123456];
signed main() {
  string s, t;
  ll n, m, k, a, b, c, cnt = 0, ans = 0;
  cin >> n;
  rep(i, n) { cin >> test[i]; }
  for (int h = n - 1; h >= 0; h--) {
    rui[h] = (rui[h + 1] + test[h]) % mod;
  }
  rep(i, n) {
    ans += (rui[i + 1] * test[i]) % mod;
    ans %= mod;
  }
  cout << ans << endl;
  return 0;
}

Fixed submission:
#include <algorithm>
#include <cassert>
#include <cmath>
#include <functional>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stack>
#include <stdio.h>
#include <string>
#include <tuple>
#include <vector>
// #include<bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define rep(i, x) for (ll i = 0; i < x; i++)
#define rep2(i, x) for (ll i = 1; i <= x; i++)
#define all(a) (a).begin(), (a).end()
using ll = long long;
using ld = long double;
using namespace std;
const ll INF = 1000000000000000000;
const ll mod = 1000000007;
const ld pi = 3.141592653589793238;

/*bool IsPrime(ll num) {
        if (num < 2) return false;
        else if (num == 2) return true;
        else if (num % 2 == 0) return false; // 偶数はあらかじめ除く
        double sqrtNum = sqrt(num);
        for (int i = 3; i <= sqrtNum; i += 2) {
                if (num % i == 0) { // 素数ではない
                        return false;
                }
        }
        // 素数である
        return true;
}*/
/*ll gcd(ll a, ll b) {
        if (a < b)swap(a, b);
        if (a % b == 0)return b;
        return gcd(b, a % b);
}
ll lcm(ll a, ll b) {
        return a / gcd(a, b) * b;
}*/
/*ll keta(ll n) {
        ll res = 0;
        while (n >= 1) {
                res += n % 10; n /= 10;
        }
        return res;
}*/
/*ll modpow(ll x, ll y, ll mod) {
        ll res = 1;
        while (y) {
                if (y % 2) { res *= x; res %= mod; }
                x = x * x % mod; y /= 2;
        }
        return res;
}*/
/*ll nCk(ll n, ll k) {
        ll a = 1, b = 1;
        for (int h = n - k + 1; h <= n; h++) { a *= h; a %= mod; }
        for (int h = 1; h <= k; h++) { b *= h; b %= mod; }
        return a * modpow(b, mod - 2) % mod;
}*/
// printf("%.10f\n", n);

ll test[223456], rui[223456];
signed main() {
  string s, t;
  ll n, m, k, a, b, c, cnt = 0, ans = 0;
  cin >> n;
  rep(i, n) { cin >> test[i]; }
  for (int h = n - 1; h >= 0; h--) {
    rui[h] = (rui[h + 1] + test[h]) % mod;
  }
  rep(i, n) {
    ans += (rui[i + 1] * test[i]) % mod;
    ans %= mod;
  }
  cout << ans << endl;
  return 0;
}