Problem p01543 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define INF 1000000000
#define MAX_V 100
#define MAX_E 1000
using namespace std;
typedef pair<int, int> P;
struct edge {
  int to, cap, cost, rev;
  edge(int to_, int cap_, int cost_, int rev_)
      : to(to_), cap(cap_), cost(cost_), rev(rev_) {}
};

int V;
vector<edge> G[MAX_V];
int h[MAX_V];
int dist[MAX_V];
int prevv[MAX_V], preve[MAX_V];

void AddEdge(int from, int to, int cap, int cost) {
  G[from].push_back(edge(to, cap, cost, G[to].size()));
  G[to].push_back(edge(from, 0, -cost, G[from].size() - 1));
}

int MinimumCostFlow(int s, int t, int f) {
  int res = 0;
  fill(h, h + V, 0);
  while (f > 0) {
    priority_queue<P, vector<P>, greater<P>> que;
    fill(dist, dist + V, INF);
    dist[s] = 0;
    que.push(P(0, s));
    while (!que.empty()) {
      P p = que.top();
      que.pop();
      int v = p.second;
      if (dist[v] < p.first)
        continue;
      for (size_t i = 0; i < G[v].size(); i++) {
        edge &e = G[v][i];
        if (e.cap > 0 && dist[e.to] > dist[v] + e.cost + h[v] - h[e.to]) {
          dist[e.to] = dist[v] + e.cost + h[v] - h[e.to];
          prevv[e.to] = v;
          preve[e.to] = i;
          que.push(P(dist[e.to], e.to));
        }
      }
    }
    if (dist[t] == INF)
      return -1;
    for (int v = 0; v < V; v++)
      h[v] += dist[v];
    int d = f;
    for (int v = t; v != s; v = prevv[v]) {
      d = min(d, G[prevv[v]][preve[v]].cap);
    }
    f -= d;
    res += d * h[t];
    for (int v = t; v != s; v = prevv[v]) {
      edge &e = G[prevv[v]][preve[v]];
      e.cap -= d;
      G[v][e.rev].cap += d;
    }
  }
  return res;
}

int main() {
  int n;
  cin >> n;
  V = n * 2 + 2;
  vector<vector<int>> W(n, vector<int>(n)), E(n, vector<int>(n));
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      cin >> W[i][j];
    }
    AddEdge(n * 2, i, 1, 0);
    AddEdge(n + i, n * 2 + 1, 1, 0);
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      cin >> E[i][j];
    }
  }
  vector<string> s(n);
  int def = 0;
  for (int i = 0; i < n; i++) {
    cin >> s[i];
    for (int j = 0; j < n; j++) {
      if (s[i][j] == '.') {
        AddEdge(i, n + j, 1, W[i][j]);
      } else {
        AddEdge(i, n + j, 1, -E[i][j]);
        def += E[i][j];
      }
    }
  }
  cout << MinimumCostFlow(n * 2, n * 2 + 1, n) + def << endl;
  int res = 0;
  for (int i = 0; i < n; i++) {
    for (auto &e : G[i]) {
      if (e.cap == 1 && e.to - n < n && s[i][e.to - n] != '.') {
        res++;
      } else if (e.cap == 0 && e.to - n < n && s[i][e.to - n] != 'o') {
        res++;
      }
    }
  }
  cout << res << endl;
  for (int i = 0; i < n; i++) {
    for (auto &e : G[i]) {
      if (e.cap == 1 && e.to - n < n && s[i][e.to - n] != '.') {
        cout << i + 1 << ' ' << e.to - n + 1 << " erase" << endl;
      } else if (e.cap == 0 && e.to - n < n && s[i][e.to - n] != 'o') {
        cout << i + 1 << ' ' << e.to - n + 1 << " write" << endl;
      }
    }
  }
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#define INF 1000000000
#define MAX_V 202
using namespace std;
typedef pair<int, int> P;
struct edge {
  int to, cap, cost, rev;
  edge(int to_, int cap_, int cost_, int rev_)
      : to(to_), cap(cap_), cost(cost_), rev(rev_) {}
};

int V;
vector<edge> G[MAX_V];
int h[MAX_V];
int dist[MAX_V];
int prevv[MAX_V], preve[MAX_V];

void AddEdge(int from, int to, int cap, int cost) {
  G[from].push_back(edge(to, cap, cost, G[to].size()));
  G[to].push_back(edge(from, 0, -cost, G[from].size() - 1));
}

int MinimumCostFlow(int s, int t, int f) {
  int res = 0;
  fill(h, h + V, 0);
  while (f > 0) {
    priority_queue<P, vector<P>, greater<P>> que;
    fill(dist, dist + V, INF);
    dist[s] = 0;
    que.push(P(0, s));
    while (!que.empty()) {
      P p = que.top();
      que.pop();
      int v = p.second;
      if (dist[v] < p.first)
        continue;
      for (size_t i = 0; i < G[v].size(); i++) {
        edge &e = G[v][i];
        if (e.cap > 0 && dist[e.to] > dist[v] + e.cost + h[v] - h[e.to]) {
          dist[e.to] = dist[v] + e.cost + h[v] - h[e.to];
          prevv[e.to] = v;
          preve[e.to] = i;
          que.push(P(dist[e.to], e.to));
        }
      }
    }
    if (dist[t] == INF)
      return -1;
    for (int v = 0; v < V; v++)
      h[v] += dist[v];
    int d = f;
    for (int v = t; v != s; v = prevv[v]) {
      d = min(d, G[prevv[v]][preve[v]].cap);
    }
    f -= d;
    res += d * h[t];
    for (int v = t; v != s; v = prevv[v]) {
      edge &e = G[prevv[v]][preve[v]];
      e.cap -= d;
      G[v][e.rev].cap += d;
    }
  }
  return res;
}

int main() {
  int n;
  cin >> n;
  V = n * 2 + 2;
  vector<vector<int>> W(n, vector<int>(n)), E(n, vector<int>(n));
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      cin >> W[i][j];
    }
    AddEdge(n * 2, i, 1, 0);
    AddEdge(n + i, n * 2 + 1, 1, 0);
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      cin >> E[i][j];
    }
  }
  vector<string> s(n);
  int def = 0;
  for (int i = 0; i < n; i++) {
    cin >> s[i];
    for (int j = 0; j < n; j++) {
      if (s[i][j] == '.') {
        AddEdge(i, n + j, 1, W[i][j]);
      } else {
        AddEdge(i, n + j, 1, -E[i][j]);
        def += E[i][j];
      }
    }
  }
  cout << MinimumCostFlow(n * 2, n * 2 + 1, n) + def << endl;
  int res = 0;
  for (int i = 0; i < n; i++) {
    for (auto &e : G[i]) {
      if (e.cap == 1 && e.to - n < n && s[i][e.to - n] != '.') {
        res++;
      } else if (e.cap == 0 && e.to - n < n && s[i][e.to - n] != 'o') {
        res++;
      }
    }
  }
  cout << res << endl;
  for (int i = 0; i < n; i++) {
    for (auto &e : G[i]) {
      if (e.cap == 1 && e.to - n < n && s[i][e.to - n] != '.') {
        cout << i + 1 << ' ' << e.to - n + 1 << " erase" << endl;
      } else if (e.cap == 0 && e.to - n < n && s[i][e.to - n] != 'o') {
        cout << i + 1 << ' ' << e.to - n + 1 << " write" << endl;
      }
    }
  }
  return 0;
}