Language: C++

#include <bits/stdc++.h>
#define FOR(i, m, n) for (int i = (m); i < (n); i++)
#define REP(i, n) FOR(i, 0, n)
using namespace std;
 
int main(void)
{
    int H, W;
    cin >> H >> W;
    vector<string> A(H);
 
    REP(i, H)
        cin >> A[i];
    
    vector<vector<int>> dp(H, vector<int>(W, H * W));
 
    REP(i, H) REP(j, W) {
        if (A[i][j] == '#')
            dp[i][j] = 0;
    }
    REP(k, max(H + W)) {
        REP(i, H) REP (j, W){
            if (i > 0)
                dp[i][j] = min(dp[i][j], dp[i - 1][j] + 1);
            if (i < H - 1)
                dp[i][j] = min(dp[i][j], dp[i + 1][j] + 1);
            if (j > 0)
                dp[i][j] = min(dp[i][j], dp[i][j - 1] + 1);
            if (j < W - 1)
                dp[i][j] = min(dp[i][j], dp[i][j + 1] + 1);
        }
    }
 
    int ans = 0;
    REP(i, H) REP(j, W) {
        ans = max(ans, dp[i][j]);
    }
    cout << ans << endl;
 
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:21:15: error: no matching function for call to 'max(int)'
   21 |     REP(k, max(H + W)) {
      |            ~~~^~~~~~~
a.cc:2:45: note: in definition of macro 'FOR'
    2 | #define FOR(i, m, n) for (int i = (m); i < (n); i++)
      |                                             ^
a.cc:21:5: note: in expansion of macro 'REP'
   21 |     REP(k, max(H + W)) {
      |     ^~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   candidate expects 2 arguments, 1 provided
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 1 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   template argument deduction/substitution failed:
a.cc:21:15: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   21 |     REP(k, max(H + W)) {
      |            ~~~^~~~~~~
a.cc:2:45: note: in definition of macro 'FOR'
    2 | #define FOR(i, m, n) for (int i = (m); i < (n); i++)
      |                                             ^
a.cc:21:5: note: in expansion of macro 'REP'
   21 |     REP(k, max(H + W)) {
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   candidate expects 2 arguments, 1 provided