Problem p02378 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <fstream>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;

#define REP(i, n) for (int i = 0; i < n; ++i)
#define FOR(i, a, b) for (int i = a; i <= b; ++i)
#define FORR(i, a, b) for (int i = a; i >= b; --i)
#define ALL(c) (c).begin(), (c).end()

typedef long long ll;
typedef vector<int> VI;
typedef vector<ll> VL;
typedef vector<VI> VVI;
typedef vector<VL> VVL;
typedef pair<int, int> P;
typedef pair<ll, ll> PL;

struct bipartite_matching {
  int n, x, y;
  VVI e;
  VI match;
  vector<bool> used;

  void init(int a, int b) {
    x = a;
    y = b;
    n = x + y;
    e.resize(n);
    match.resize(n);
    used.resize(n);
  }

  void add_edge(int u, int v) {
    e[u].push_back(v + x);
    e[v + x].push_back(u);
  }

  bool dfs(int v) {
    used[v] = true;
    for (int u : e[v]) {
      int w = match[u];
      if (w < 0 || (!used[w] && dfs(w))) {
        match[v] = u;
        match[u] = v;
        return true;
      }
    }
    return false;
  }

  int calc_matching() {
    int res = 0;
    fill(ALL(match), -1);
    REP(v, n) {
      if (match[v] < 0) {
        used.assign(n, 0);
        if (dfs(v))
          res++;
      }
    }
    return res;
  }
};

int main() {
  int n, m, e;
  cin >> n >> m >> e;

  cout << 3 << endl;

  bipartite_matching bm;
  bm.init(n, m);

  REP(_, e) {
    int u, v;
    scanf("%d %d", &u, &v);
    bm.add_edge(u, v);
  }

  cout << bm.calc_matching() << endl;

  return 0;
}

Fixed submission:
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <fstream>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;

#define REP(i, n) for (int i = 0; i < n; ++i)
#define FOR(i, a, b) for (int i = a; i <= b; ++i)
#define FORR(i, a, b) for (int i = a; i >= b; --i)
#define ALL(c) (c).begin(), (c).end()

typedef long long ll;
typedef vector<int> VI;
typedef vector<ll> VL;
typedef vector<VI> VVI;
typedef vector<VL> VVL;
typedef pair<int, int> P;
typedef pair<ll, ll> PL;

struct bipartite_matching {
  int n, x, y;
  VVI e;
  VI match;
  vector<bool> used;

  void init(int a, int b) {
    x = a;
    y = b;
    n = x + y;
    e.resize(n);
    match.resize(n);
    used.resize(n);
  }

  void add_edge(int u, int v) {
    e[u].push_back(v + x);
    e[v + x].push_back(u);
  }

  bool dfs(int v) {
    used[v] = true;
    for (int u : e[v]) {
      int w = match[u];
      if (w < 0 || (!used[w] && dfs(w))) {
        match[v] = u;
        match[u] = v;
        return true;
      }
    }
    return false;
  }

  int calc_matching() {
    int res = 0;
    fill(ALL(match), -1);
    REP(v, n) {
      if (match[v] < 0) {
        used.assign(n, 0);
        if (dfs(v))
          res++;
      }
    }
    return res;
  }
};

int main() {
  int n, m, e;
  cin >> n >> m >> e;

  // cout << 3 << endl;
  // return 0;

  bipartite_matching bm;
  bm.init(n, m);

  REP(_, e) {
    int u, v;
    scanf("%d %d", &u, &v);
    bm.add_edge(u, v);
  }

  cout << bm.calc_matching() << endl;

  return 0;
}