Language: C++

#define _GLIBCXX_DEBUG
// #pragma GCC optimize ("trapv") // kills the program on integer overﬂows (but is really slow).
#include <bits/stdc++.h>
using namespace std;
using namespace std::chrono;

#define ll long long
#define ull unsigned long long
#define FIO ios_base::sync_with_stdio(false);cin.tie(NULL);
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define ff first
#define ss second
#define vt vector
#define vll vt<ll>
#define pll pair<ll,ll>
#define vpll vt<pll>
#define vvll vt<vll>
#define all(v) v.begin(),v.end()
#define FOR(i,n) for(ll i=0;i<n;i++)
#define ffo(i,a,b) for(ll i=a;i<=b;i++)
#define rfo(i,a,b) for(ll i=a;i>=b;i--)
#define space cout<<"\n\n";
#define endl "\n"
#define pqmx priority_queue<ll>
#define pqmn priority_queue<ll,vll,greater<ll>>
#define fps(x,y) fixed<<setprecision(y)<<x
#define merg(a,b,c) set_union(a.begin(),a.end(),b.begin(),b.end(),inserter(c,c.begin()))
#define set_ar(arr,v) memset(arr,v,sizeof(arr))
#define go_t int testcases; cin>>testcases; ffo(caseno,1,testcases)

#define ctime auto start = high_resolution_clock::now()
#define etime auto stop = high_resolution_clock::now()
#define ptime auto z1z = duration_cast<microseconds>(stop-start); cout<<"Time elapsed : "<<z1z.count()<<" microseconds\n"

#define dbg1(x)             cout <<#x<<": "<<x<<'\n';
#define dbg2(x, y)          cout <<#x<<": "<<x<<" | "<<#y<<": "<<y<<'\n';
#define dbg3(x, y, z)       cout <<#x<<": "<<x<<" | "<<#y<<": "<<y<<" | "<<#z<<": "<<z<<'\n';
#define dbg4(a, b, c, d)    cout <<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<'\n';
#define dbg5(a, b, c, d, e) cout <<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<" | "<<#e<<": "<<e<<'\n';

const ll mod = 1e9 + 7;
const ll N = 3e3 + 6;
const ll maxN = 1e4 + 5;
const ll MAX_SIZE = 2e6 + 6;
const ll INF = 0x3f3f3f3f3f3f3f3fll;
const double PI = 3.14159265359;

ll powerM(ll x, ll y, ll M = mod) { // default argument
	ll v = 1; x = x % M; while (y > 0) {if (y & 1)v = (v * x) % M; y = y >> 1; x = (x * x) % M;} return v;
}

ll power(ll x, ll y) {
	ll v = 1; while (y > 0) {if (y & 1)v = v * x; y = y >> 1; x = x * x;} return v;
}

int dx[4] = { -1, 0, 1, 0};
int dy[4] = {0, 1, 0, -1};
// up, right, down, left
int mx = 3e5 + 10;
ll mid[mx];
ll row[mx];
ll col[mx];

int main()
{
#ifndef ONLINE_JUDGE
	freopen("in3.txt", "r", stdin);
	freopen("out2.txt", "w", stdout);
#endif
	FIO
	ll h, w, m;
	cin >> h >> w >> m;
	ll hi, wi;
	ll
	map<pll, ll> mp;
	FOR(i, m) {
		cin >> hi >> wi;
		mp[ {hi, wi}]++;
		if (hi == wi) {
			mid[hi]++;
		}
		row[hi]++;
		col[hi]++;
	}
	ll ans = 0;
	ll v1 = 0, v2 = 0;
	ll pr = 0, pc = 0;
	set<ll> pps;
	for (int i = 1; i <= 3e5; ++i) {
		if (row[i] > v1) {
			pps.clear();
			pps.insert(i);
			v1 = row[i];
		}
		else if (row[i] == v1) {
			pps.insert(i);
		}
	}
	for(auto it : pps){
		ans = max(ans, v1 + col[it] - mp[{it,c}]);
	}
	cout << ans;
	return 0;
}

Compiler output:
a.cc:62:8: error: size of array 'mid' is not an integral constant-expression
   62 | ll mid[mx];
      |        ^~
a.cc:63:8: error: size of array 'row' is not an integral constant-expression
   63 | ll row[mx];
      |        ^~
a.cc:64:8: error: size of array 'col' is not an integral constant-expression
   64 | ll col[mx];
      |        ^~
a.cc: In function 'int main()':
a.cc:12:12: error: invalid declarator before 'make_pair'
   12 | #define mp make_pair
      |            ^~~~~~~~~
a.cc:77:22: note: in expansion of macro 'mp'
   77 |         map<pll, ll> mp;
      |                      ^~
a.cc:80:19: error: invalid types '<unresolved overloaded function type>[<brace-enclosed initializer list>]' for array subscript
   80 |                 mp[ {hi, wi}]++;
      |                   ^
a.cc:102:54: error: 'c' was not declared in this scope; did you mean 'pc'?
  102 |                 ans = max(ans, v1 + col[it] - mp[{it,c}]);
      |                                                      ^
      |                                                      pc
a.cc:102:49: error: invalid types '<unresolved overloaded function type>[<brace-enclosed initializer list>]' for array subscript
  102 |                 ans = max(ans, v1 + col[it] - mp[{it,c}]);
      |                                                 ^