Problem p01090 (C++)

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

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const ll inf = 1LL << 62;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

using P = tuple<int, int, int>;

int n, k;

struct UnionFind {
  vector<int> data;
  UnionFind(int size) : data(size, -1) {}
  bool unionSet(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) {
      if (data[y] < data[x])
        swap(x, y);
      data[x] += data[y];
      data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) { return root(x) == root(y); }
  int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
  int size(int x) { return -data[root(x)]; }
};

using Elem = tuple<int, int, int, int>;

int kruskal(vector<vector<P>> graph, int diff) {
  vi a_cnt(2);
  rep(v, n) for (auto &e : graph[v]) if (get<1>(e) == 0) get<0>(e) += diff;
  int ret = 0;
  rep(ai, 2) {
    priority_queue<Elem, vector<Elem>, greater<Elem>> q;
    rep(v, n) {
      for (auto &e : graph[v]) {
        int u, w, l;
        tie(w, l, u) = e;

        l *= -1;
        e = P(w, l, u);
        assert(l == 0 or l == 1 or l == -1);

        if (v < u) {
          q.push(Elem(w, l, u, v));
        }
      }
    }

    UnionFind uf(n);
    ret = 0;
    int cnt = 0;
    while (q.size()) {
      int w, l, v, u;
      tie(w, l, v, u) = q.top();
      q.pop();

      assert(l == 0 or l == 1 or l == -1);

      if (uf.findSet(v, u))
        continue;
      uf.unionSet(v, u);
      cnt++;

      ret += w;
      if (l == 0) {
        a_cnt[ai]++;
      }
    }
    assert(cnt == n - 1);
  }

  ret -= diff * k;
  if (a_cnt[0] > a_cnt[1])
    swap(a_cnt[0], a_cnt[1]);

  // cerr << a_cnt << endl;
  if (not(a_cnt[0] <= k and k <= a_cnt[1]))
    ret = (a_cnt[1] > k ? -1 : -2);

  return ret;
}

int offset = 10000;

int main(void) {
  for (int m; cin >> n >> m >> k, n;) {
    vector<vector<P>> graph(n);
    rep(loop, m) {
      int u, v, w;
      char l;
      cin >> u >> v >> w >> l;
      u--, v--, w += offset;
      assert(0 <= u and u < n and 0 <= v and v < n);

      graph[u].push_back(P(w, l == 'A' ? 0 : 1, v));
      graph[v].push_back(P(w, l == 'A' ? 0 : 1, u));
    }

    int lb = -offset, ub = offset;
    int res = -1;
    rep(loop, 100) {
      int mid = (lb + ub) / 2;

      int ret = kruskal(graph, mid);
      if (ret == -2) {
        ub = mid;
      } else if (ret == -1) {
        lb = mid;
      } else {
        res = ret - (offset * (n - 1));
        break;
      }
    }

    cout << res << endl;
  }

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const ll inf = 1LL << 62;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

using P = tuple<int, int, int>;

int n, k;

struct UnionFind {
  vector<int> data;
  UnionFind(int size) : data(size, -1) {}
  bool unionSet(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) {
      if (data[y] < data[x])
        swap(x, y);
      data[x] += data[y];
      data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) { return root(x) == root(y); }
  int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
  int size(int x) { return -data[root(x)]; }
};

using Elem = tuple<int, int, int, int>;

int kruskal(vector<vector<P>> graph, int diff) {
  vi a_cnt(2);
  rep(v, n) for (auto &e : graph[v]) if (get<1>(e) == 0) get<0>(e) += diff;
  int ret = 0;
  rep(ai, 2) {
    priority_queue<Elem, vector<Elem>, greater<Elem>> q;
    rep(v, n) {
      for (auto &e : graph[v]) {
        int u, w, l;
        tie(w, l, u) = e;

        l *= -1;
        e = P(w, l, u);
        assert(l == 0 or l == 1 or l == -1);

        if (v < u) {
          q.push(Elem(w, l, u, v));
        }
      }
    }

    UnionFind uf(n);
    ret = 0;
    int cnt = 0;
    while (q.size()) {
      int w, l, v, u;
      tie(w, l, v, u) = q.top();
      q.pop();

      assert(l == 0 or l == 1 or l == -1);

      if (uf.findSet(v, u))
        continue;
      uf.unionSet(v, u);
      cnt++;

      ret += w;
      if (l == 0) {
        a_cnt[ai]++;
      }
    }
    if (cnt != n - 1) {
      return -1;
    }
  }

  ret -= diff * k;
  if (a_cnt[0] > a_cnt[1])
    swap(a_cnt[0], a_cnt[1]);

  // cerr << a_cnt << endl;
  if (not(a_cnt[0] <= k and k <= a_cnt[1]))
    ret = (a_cnt[1] > k ? -1 : -2);

  return ret;
}

int offset = 10000;

int main(void) {
  for (int m; cin >> n >> m >> k, n;) {
    vector<vector<P>> graph(n);
    rep(loop, m) {
      int u, v, w;
      char l;
      cin >> u >> v >> w >> l;
      u--, v--, w += offset;
      assert(0 <= u and u < n and 0 <= v and v < n);

      graph[u].push_back(P(w, l == 'A' ? 0 : 1, v));
      graph[v].push_back(P(w, l == 'A' ? 0 : 1, u));
    }

    int lb = -offset, ub = offset;
    int res = -1;
    rep(loop, 100) {
      int mid = (lb + ub) / 2;

      int ret = kruskal(graph, mid);
      if (ret == -2) {
        ub = mid;
      } else if (ret == -1) {
        lb = mid;
      } else {
        res = ret - (offset * (n - 1));
        break;
      }
    }

    cout << res << endl;
  }

  return 0;
}