Problem p02735 (C++)

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

#define li long long int
#define rep(i, to) for (li i = 0; i < ((li)(to)); i++)
#define repp(i, start, to) for (li i = (li)(start); i < ((li)(to)); i++)
#define pb push_back
#define sz(v) ((li)(v).size())
#define bgn(v) ((v).begin())
#define eend(v) ((v).end())
#define allof(v) (v).begin(), (v).end()
#define dodp(v, n) memset(v, (li)n, sizeof(v))
#define bit(n) (1ll << (li)(n))
#define mp(a, b) make_pair(a, b)
#define rin rep(i, n)
#define EPS 1e-12
#define ETOL 1e-8
#define MOD 1000000007
typedef pair<li, li> PI;

#define INF bit(60)

#define DBGP 1

#define idp if (DBGP)
#define F first
#define S second
#define p2(a, b) idp cout << a << "\t" << b << endl
#define p3(a, b, c) idp cout << a << "\t" << b << "\t" << c << endl
#define p4(a, b, c, d)                                                         \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << endl
#define p5(a, b, c, d, e)                                                      \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << endl
#define p6(a, b, c, d, e, f)                                                   \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << endl
#define p7(a, b, c, d, e, f, g)                                                \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << endl
#define p8(a, b, c, d, e, f, g, h)                                             \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << endl
#define p9(a, b, c, d, e, f, g, h, i)                                          \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << "\t" << i << endl
#define p10(a, b, c, d, e, f, g, h, i, j)                                      \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << "\t" << i << "\t" << j << endl
#define foreach(it, v)                                                         \
  for (__typeof((v).begin()) it = (v).begin(); it != (v).end(); ++it)
#define p2p(x) idp p2((x).F, (x).S)
#define dump(x, n)                                                             \
  idp {                                                                        \
    rep(i, n) { cout << x[i] << " "; }                                         \
    puts("");                                                                  \
  }
#define dump2(x, n)                                                            \
  idp {                                                                        \
    rep(i, n) { cout << "[" << x[i].F << " , " << x[i].S << "] "; }            \
    puts("");                                                                  \
  }
#define dumpi(x)                                                               \
  idp {                                                                        \
    foreach (it, x) {                                                          \
      cout << (*it) << " ";                                                    \
    }                                                                          \
    puts("");                                                                  \
  }
#define dumpi2(x)                                                              \
  idp {                                                                        \
    foreach (it, x) {                                                          \
      cout << "[" << (it)->F << " , " << (it)->S << "] ";                      \
    }                                                                          \
    puts("");                                                                  \
  }

#define read2d(a, w, h) rep(i, h) rep(j, w) cin >> a[i][j]
#define dump2d(a, w, h)                                                        \
  rep(i, h) {                                                                  \
    rep(j, w) cout << a[i][j] << " ";                                          \
    puts("");                                                                  \
  }

typedef pair<li, li> PI;

li cost[111][111];
li h, w;

li dx[] = {1, 0};
li dy[] = {0, 1};

string board[111];

inline li dijkstra() {
  priority_queue<pair<li, PI>> pq;
  pq.push({0, {0, 0}});
  while (!pq.empty()) {
    PI now = pq.top().S;
    li now_cost = -pq.top().F;
    pq.pop();
    if (now_cost >= cost[now.F][now.S]) {
      continue;
    }
    cost[now.F][now.S] = now_cost;
    if (now.F == h - 1 && now.S == w - 1) {
      return now_cost;
    }
    rep(k, 4) {
      PI next = {now.F + dy[k], now.S + dx[k]};
      if (min(next.F, next.S) < 0 || next.F >= h || next.S >= w) {
        continue;
      }
      if (board[next.F][next.S] != board[now.F][now.S]) {
        pq.emplace(-now_cost - 1, next);
      } else {
        pq.emplace(-now_cost, next);
      }
    }
  }
  return INF;
}

int main() {
  cin >> h >> w;
  rep(i, h) { cin >> board[i]; }
  rep(i, h) {
    rep(j, w) { cost[i][j] = INF; }
  }
  li res = dijkstra();
  if (res % 2 == 0) {
    res /= 2;
    if (board[0][0] == '#') {
      ++res;
    }
  } else {
    res = (res + 1) / 2;
  }
  cout << res << endl;

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;

#define li long long int
#define rep(i, to) for (li i = 0; i < ((li)(to)); i++)
#define repp(i, start, to) for (li i = (li)(start); i < ((li)(to)); i++)
#define pb push_back
#define sz(v) ((li)(v).size())
#define bgn(v) ((v).begin())
#define eend(v) ((v).end())
#define allof(v) (v).begin(), (v).end()
#define dodp(v, n) memset(v, (li)n, sizeof(v))
#define bit(n) (1ll << (li)(n))
#define mp(a, b) make_pair(a, b)
#define rin rep(i, n)
#define EPS 1e-12
#define ETOL 1e-8
#define MOD 1000000007
typedef pair<li, li> PI;

#define INF bit(60)

#define DBGP 1

#define idp if (DBGP)
#define F first
#define S second
#define p2(a, b) idp cout << a << "\t" << b << endl
#define p3(a, b, c) idp cout << a << "\t" << b << "\t" << c << endl
#define p4(a, b, c, d)                                                         \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << endl
#define p5(a, b, c, d, e)                                                      \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << endl
#define p6(a, b, c, d, e, f)                                                   \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << endl
#define p7(a, b, c, d, e, f, g)                                                \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << endl
#define p8(a, b, c, d, e, f, g, h)                                             \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << endl
#define p9(a, b, c, d, e, f, g, h, i)                                          \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << "\t" << i << endl
#define p10(a, b, c, d, e, f, g, h, i, j)                                      \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << "\t" << i << "\t" << j << endl
#define foreach(it, v)                                                         \
  for (__typeof((v).begin()) it = (v).begin(); it != (v).end(); ++it)
#define p2p(x) idp p2((x).F, (x).S)
#define dump(x, n)                                                             \
  idp {                                                                        \
    rep(i, n) { cout << x[i] << " "; }                                         \
    puts("");                                                                  \
  }
#define dump2(x, n)                                                            \
  idp {                                                                        \
    rep(i, n) { cout << "[" << x[i].F << " , " << x[i].S << "] "; }            \
    puts("");                                                                  \
  }
#define dumpi(x)                                                               \
  idp {                                                                        \
    foreach (it, x) {                                                          \
      cout << (*it) << " ";                                                    \
    }                                                                          \
    puts("");                                                                  \
  }
#define dumpi2(x)                                                              \
  idp {                                                                        \
    foreach (it, x) {                                                          \
      cout << "[" << (it)->F << " , " << (it)->S << "] ";                      \
    }                                                                          \
    puts("");                                                                  \
  }

#define read2d(a, w, h) rep(i, h) rep(j, w) cin >> a[i][j]
#define dump2d(a, w, h)                                                        \
  rep(i, h) {                                                                  \
    rep(j, w) cout << a[i][j] << " ";                                          \
    puts("");                                                                  \
  }

typedef pair<li, li> PI;

li cost[111][111];
li h, w;

li dx[] = {1, 0};
li dy[] = {0, 1};

string board[111];

inline li dijkstra() {
  priority_queue<pair<li, PI>> pq;
  pq.push({0, {0, 0}});
  while (!pq.empty()) {
    PI now = pq.top().S;
    li now_cost = -pq.top().F;
    pq.pop();
    if (now_cost >= cost[now.F][now.S]) {
      continue;
    }
    cost[now.F][now.S] = now_cost;
    if (now.F == h - 1 && now.S == w - 1) {
      return now_cost;
    }
    rep(k, 2) {
      PI next = {now.F + dy[k], now.S + dx[k]};
      if (min(next.F, next.S) < 0 || next.F >= h || next.S >= w) {
        continue;
      }
      if (board[next.F][next.S] != board[now.F][now.S]) {
        pq.emplace(-now_cost - 1, next);
      } else {
        pq.emplace(-now_cost, next);
      }
    }
  }
  return INF;
}

int main() {
  cin >> h >> w;
  rep(i, h) { cin >> board[i]; }
  rep(i, h) {
    rep(j, w) { cost[i][j] = INF; }
  }
  li res = dijkstra();
  if (res % 2 == 0) {
    res /= 2;
    if (board[0][0] == '#') {
      ++res;
    }
  } else {
    res = (res + 1) / 2;
  }
  cout << res << endl;

  return 0;
}