Problem p02364 (C++)

Buggy submission (status: Runtime Error):
#include <assert.h>
#include <stdio.h>

namespace beet {

template <typename T> void swap(T &a, T &b) {
  T x = a;
  a = b;
  b = x;
}

template <typename T> struct Vector {
  int sz, cap;
  T *data;
  Vector() : sz(0), cap(1) { data = new T[cap]; }
  Vector(int sz) : sz(sz), cap(sz << 1) { data = new T[cap]; }
  Vector(int sz, T t) : sz(sz), cap(sz << 1) {
    data = new T[cap];
    for (int i = 0; i < sz; i++)
      data[i] = t;
  }
  ~Vector() { delete[] data; }
  void resolve() {
    T *tmp = new T[cap];
    for (int i = 0; i < sz; i++)
      tmp[i] = data[i];
    delete[] data;
    data = tmp;
  }
  void resize(int nsz) {
    cap = nsz << 1;
    if (sz > cap)
      sz = cap;
    resolve();
  }
  void assign(int nsz, T t) {
    resize(nsz);
    sz = nsz;
    for (int i = 0; i < sz; i++)
      data[i] = t;
  }
  void push_back(T x) {
    if (sz >= cap) {
      cap <<= 1;
      assert(sz < cap);
      resolve();
    }
    data[sz++] = x;
  }
  void pop_back() { sz--; }
  int size() const { return sz; }
  const T operator[](int x) const { return data[x]; }
  T &operator[](int x) {
    assert(0 <= x && x < sz);
    return data[x];
  }
};

template <typename T> void sort(Vector<T> &vs) {
  int n = vs.size();
  Vector<T> tmp(n);

  auto dfs = [&](int l, int r, auto &func) -> void {
    // printf("%d %d\n",l,r);
    if (l + 1 == r)
      return;
    int m = (l + r) >> 1;
    func(l, m, func);
    func(m, r, func);
    for (int k = l; k < r; k++)
      tmp[k] = vs[k];

    int i = l, j = m, k = l;
    while (i < m && j < r) {
      if (tmp[i] < tmp[j]) {
        vs[k++] = tmp[i++];
      } else {
        vs[k++] = tmp[j++];
      }
    }
    while (i < m)
      vs[k++] = tmp[i++];
    while (j < r)
      vs[k++] = tmp[j++];
  };
  dfs(0, n, dfs);
}

template <typename T> struct Kruskal {

  struct edge {
    int from, to;
    T cost;
    int used;
    edge() {}
    edge(int from, int to, T cost) : from(from), to(to), cost(cost), used(0) {}
    bool operator<(const edge &e) const { return cost < e.cost; }
  };

  int n;
  Vector<int> r, p;
  Vector<edge> es;

  Kruskal() {}
  Kruskal(int n) : n(n), r(n, 1), p(n) {
    for (int i = 0; i < n; i++)
      p[i] = i;
  }

  int find(int x) { return (x == p[x] ? x : p[x] = find(p[x])); }

  bool same(int x, int y) { return find(x) == find(y); }

  void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y)
      return;
    if (r[x] < r[y])
      swap(x, y);
    r[x] += r[y];
    p[y] = x;
  }

  void add_edge(int u, int v, T c) { es.push_back(edge(u, v, c)); }

  T build() {
    sort(es);
    T res = 0;
    for (int i = 0; i < (int)es.size(); i++) {
      auto &e = es[i];
      if (!same(e.from, e.to)) {
        res += e.cost;
        unite(e.from, e.to);
        e.used = 1;
      }
    }
    return res;
  }
};

} // namespace beet

// INSERT ABOVE HERE
using namespace beet;

int main() {
  int n, m;
  scanf("%d %d", &n, &m);

  Kruskal<int> mst(n);
  for (int i = 0; i < m; i++) {
    int s, t, w;
    scanf("%d %d %d", &s, &t, &w);
    mst.add_edge(s, t, w);
  }

  printf("%d\n", mst.build());
  return 0;
}


Fixed submission:
#include <assert.h>
#include <stdio.h>

namespace beet {

template <typename T> void swap(T &a, T &b) {
  T x = a;
  a = b;
  b = x;
}

template <typename T> struct Vector {
  int sz, cap;
  T *data;
  Vector() : sz(0), cap(1) { data = new T[cap]; }
  Vector(int sz) : sz(sz), cap(sz << 1) { data = new T[cap]; }
  Vector(int sz, T t) : sz(sz), cap(sz << 1) {
    data = new T[cap];
    for (int i = 0; i < sz; i++)
      data[i] = t;
  }
  ~Vector() { delete[] data; }
  void resolve() {
    T *tmp = new T[cap];
    for (int i = 0; i < sz; i++)
      tmp[i] = data[i];
    delete[] data;
    data = tmp;
  }
  void resize(int nsz) {
    cap = nsz << 1;
    if (sz > cap)
      sz = cap;
    resolve();
  }
  void assign(int nsz, T t) {
    resize(nsz);
    sz = nsz;
    for (int i = 0; i < sz; i++)
      data[i] = t;
  }
  void push_back(T x) {
    if (sz >= cap) {
      cap <<= 1;
      assert(sz < cap);
      resolve();
    }
    data[sz++] = x;
  }
  void pop_back() { sz--; }
  int size() const { return sz; }
  const T operator[](int x) const { return data[x]; }
  T &operator[](int x) {
    assert(0 <= x && x < sz);
    return data[x];
  }
};

template <typename T> void sort(Vector<T> &vs) {
  if (vs.size() == 0)
    return;

  int n = vs.size();
  Vector<T> tmp(n);

  auto dfs = [&](int l, int r, auto &func) -> void {
    // printf("%d %d\n",l,r);
    if (l + 1 == r)
      return;
    int m = (l + r) >> 1;
    func(l, m, func);
    func(m, r, func);
    for (int k = l; k < r; k++)
      tmp[k] = vs[k];

    int i = l, j = m, k = l;
    while (i < m && j < r) {
      if (tmp[i] < tmp[j]) {
        vs[k++] = tmp[i++];
      } else {
        vs[k++] = tmp[j++];
      }
    }
    while (i < m)
      vs[k++] = tmp[i++];
    while (j < r)
      vs[k++] = tmp[j++];
  };
  dfs(0, n, dfs);
}

template <typename T> struct Kruskal {

  struct edge {
    int from, to;
    T cost;
    int used;
    edge() {}
    edge(int from, int to, T cost) : from(from), to(to), cost(cost), used(0) {}
    bool operator<(const edge &e) const { return cost < e.cost; }
  };

  int n;
  Vector<int> r, p;
  Vector<edge> es;

  Kruskal() {}
  Kruskal(int n) : n(n), r(n, 1), p(n) {
    for (int i = 0; i < n; i++)
      p[i] = i;
  }

  int find(int x) { return (x == p[x] ? x : p[x] = find(p[x])); }

  bool same(int x, int y) { return find(x) == find(y); }

  void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y)
      return;
    if (r[x] < r[y])
      swap(x, y);
    r[x] += r[y];
    p[y] = x;
  }

  void add_edge(int u, int v, T c) { es.push_back(edge(u, v, c)); }

  T build() {
    sort(es);
    T res = 0;
    for (int i = 0; i < (int)es.size(); i++) {
      auto &e = es[i];
      if (!same(e.from, e.to)) {
        res += e.cost;
        unite(e.from, e.to);
        e.used = 1;
      }
    }
    return res;
  }
};

} // namespace beet

// INSERT ABOVE HERE
using namespace beet;

int main() {
  int n, m;
  scanf("%d %d", &n, &m);

  Kruskal<int> mst(n);
  for (int i = 0; i < m; i++) {
    int s, t, w;
    scanf("%d %d %d", &s, &t, &w);
    mst.add_edge(s, t, w);
  }

  printf("%d\n", mst.build());
  return 0;
}