Problem p03096 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

// types
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
typedef vector<ll> vll;

// macros
#define ALL(a) a.begin(), a.end()
#define SZ(a) ((int)a.size())
#define FI first
#define SE second
#define REP(i, n) for (int i = 0; i < ((int)n); i++)
#define REP1(i, n) for (int i = 1; i < ((int)n); i++)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define PB push_back
#define EB emplace_back
#define MP(a, b) make_pair(a, b)
#define SORT_UNIQUE(c)                                                         \
  (sort(c.begin(), c.end()),                                                   \
   c.resize(distance(c.begin(), unique(c.begin(), c.end()))))
#define GET_POS(c, x) (lower_bound(c.begin(), c.end(), x) - c.begin())
#define Decimal fixed << setprecision(20)
#define INF 1000000000
#define LLINF 1000000000000000000LL

// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double eps = 1e-10;
const int MOD = 1e9 + 7;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  ll n;
  cin >> n;
  vll c(n);
  REP(i, n) {
    cin >> c[i];
    c[i]--;
  }

  vll dp(n + 1, 0);
  dp[0] = 1;
  vll color(n + 1, -1);
  REP(i, n) {
    ll x = color[c[i]];
    if (x == -1) {
      dp[i + 1] = dp[i];
    } else {
      if (x == i - 1)
        dp[i + 1] = dp[i];
      else
        dp[i + 1] = (dp[x + 1] + dp[i]) % MOD;
    }

    color[c[i]] = i;
  }

  cout << dp[n] << endl;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

// types
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
typedef vector<ll> vll;

// macros
#define ALL(a) a.begin(), a.end()
#define SZ(a) ((int)a.size())
#define FI first
#define SE second
#define REP(i, n) for (int i = 0; i < ((int)n); i++)
#define REP1(i, n) for (int i = 1; i < ((int)n); i++)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define PB push_back
#define EB emplace_back
#define MP(a, b) make_pair(a, b)
#define SORT_UNIQUE(c)                                                         \
  (sort(c.begin(), c.end()),                                                   \
   c.resize(distance(c.begin(), unique(c.begin(), c.end()))))
#define GET_POS(c, x) (lower_bound(c.begin(), c.end(), x) - c.begin())
#define Decimal fixed << setprecision(20)
#define INF 1000000000
#define LLINF 1000000000000000000LL

// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double eps = 1e-10;
const int MOD = 1e9 + 7;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  ll n;
  cin >> n;
  vll c(n);
  REP(i, n) {
    cin >> c[i];
    c[i]--;
  }

  vll dp(n + 1, 0);
  dp[0] = 1;
  vll color(2 * 1e5 + 1, -1);
  REP(i, n) {
    ll x = color[c[i]];
    if (x == -1) {
      dp[i + 1] = dp[i];
    } else {
      if (x == i - 1)
        dp[i + 1] = dp[i];
      else
        dp[i + 1] = (dp[x + 1] + dp[i]) % MOD;
    }

    color[c[i]] = i;
  }

  cout << dp[n] << endl;
}