Problem p03634 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
// #pragma GCC optimize("Ofast")
// #define _GLIBCXX_DEBUG
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
// #define int ll
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef pair<int, int> pii;
typedef vector<pair<int, int>> vpii;
typedef vector<vector<int>> vvi;
typedef vector<vector<char>> vvc;
typedef vector<vector<string>> vvs;
typedef vector<vector<ll>> vvll;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define irep(it, stl) for (auto it = stl.begin(); it != stl.end(); it++)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define mp(p, q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define floatprec(dig) fixed << setprecision(dig)
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define itn int;
#define invar(typ, var)                                                        \
  typ var;                                                                     \
  cin >> var;
int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
struct io {
  io() {
    ios::sync_with_stdio(false);
    cin.tie(0);
  }
};
const int INF = INT_MAX / 2;
const ll LLINF = 1LL << 60;
constexpr ll MOD = 1000000007;
const double EPS = 1e-9;

struct edge {
  ll from;
  ll to;
  ll cost;
};

void dfs(vector<vector<edge>> &edges, vll &dist, ll ck, unordered_set<ll> seen,
         ll cdist) {
  dist[ck] = cdist;
  for (auto ed : edges[ck]) {
    if (seen.find(ed.to) == seen.end()) {
      seen.emplace(ed.to);
      dfs(edges, dist, ed.to, seen, cdist + ed.cost);
    }
  }
}

signed main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll N;
  cin >> N;

  vector<vector<edge>> edges(N, vector<edge>());

  rep(i, N - 1) {
    ll a;
    ll b;
    ll c;
    cin >> a >> b >> c;
    a--;
    b--;
    edges[a].push_back({a, b, c});
    edges[b].push_back({b, a, c});
  }

  ll Q;
  ll K;
  cin >> Q >> K;

  K--;
  // 前計算
  vector<ll> dist(N);
  unordered_set<ll> seen;
  seen.emplace(K);
  dfs(edges, dist, K, seen, 0);

  rep(i, Q) {
    ll x;
    ll y;
    cin >> x >> y;
    x--;
    y--;
    ll r = dist[x] + dist[y];
    fin(r);
  }
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
// #pragma GCC optimize("Ofast")
// #define _GLIBCXX_DEBUG
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
// #define int ll
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef pair<int, int> pii;
typedef vector<pair<int, int>> vpii;
typedef vector<vector<int>> vvi;
typedef vector<vector<char>> vvc;
typedef vector<vector<string>> vvs;
typedef vector<vector<ll>> vvll;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define irep(it, stl) for (auto it = stl.begin(); it != stl.end(); it++)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define mp(p, q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define floatprec(dig) fixed << setprecision(dig)
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define itn int;
#define invar(typ, var)                                                        \
  typ var;                                                                     \
  cin >> var;
int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
struct io {
  io() {
    ios::sync_with_stdio(false);
    cin.tie(0);
  }
};
const int INF = INT_MAX / 2;
const ll LLINF = 1LL << 60;
constexpr ll MOD = 1000000007;
const double EPS = 1e-9;

struct edge {
  ll from;
  ll to;
  ll cost;
};

void dfs(vector<vector<edge>> &edges, vll &dist, ll ck, unordered_set<ll> &seen,
         ll cdist) {
  dist[ck] = cdist;
  for (auto ed : edges[ck]) {
    if (seen.find(ed.to) == seen.end()) {
      seen.emplace(ed.to);
      dfs(edges, dist, ed.to, seen, cdist + ed.cost);
    }
  }
}

signed main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll N;
  cin >> N;

  vector<vector<edge>> edges(N, vector<edge>());

  rep(i, N - 1) {
    ll a;
    ll b;
    ll c;
    cin >> a >> b >> c;
    a--;
    b--;
    edges[a].push_back({a, b, c});
    edges[b].push_back({b, a, c});
  }

  ll Q;
  ll K;
  cin >> Q >> K;

  K--;
  // 前計算
  vector<ll> dist(N);
  unordered_set<ll> seen;
  seen.emplace(K);
  dfs(edges, dist, K, seen, 0);

  rep(i, Q) {
    ll x;
    ll y;
    cin >> x >> y;
    x--;
    y--;
    ll r = dist[x] + dist[y];
    fin(r);
  }
}