Language: C++

#include<iostream>
#include<fstream>
#include<sstream>
#include<algorithm>
#include<vector>
#include<queue>
#include<map>
#include<set>
#include<string>
#include<cmath>
#include<cstdio>
#include<cassert>
using namespace std;

#define REP(i,m,n) for(int i=(m); i<(int)(n); i++)
#define RREP(i,m,n) for(int i=(int)(n-1); i>=m; i--)
#define rep(i,n) REP(i,0,n)
#define rrep(i,n) RREP(i,0,n)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define aut(r,v) __typeof(v) r = (v)
#define each(it,o) for(aut(it,(o).begin()); it!=(o).end(); ++it)
#define reach(it,o) for(aut(it,(o).rbegin()); it!=(o).rend(); ++it)
#define fi first
#define se second
#define debug(...) {cerr<<"[L"<<__LINE__<<"] "; _debug(__VA_ARGS__);}

template<typename T1, typename T2> ostream& operator<<(ostream& o, const pair<T1, T2>& p)
{return o<<"("<<p.first<<", "<<p.second<<")";}
template<typename T>string join(const vector<T>&v, string del=", ")
{stringstream s;rep(i,v.size())s<<del<<v[i];return s.str().substr(del.size());}
template<typename T>ostream& operator<<(ostream& o, const vector<T>&v)
{if(v.size())o<<"["<<join(v)<<"]";return o;}
template<typename T>ostream& operator<<(ostream& o, const vector<vector<T> >&vv)
{int l=vv.size();if(l){o<<endl;rep(i,l){o<<(i==0?"[ ":",\n  ")<<vv[i]<<(i==l-1?" ]":"");}}return o;}
template<typename T>ostream& operator<<(ostream& o, const set<T>& st)
{vector<T> v(st.begin(),st.end());o<<"{ "<<join(v)<<" }";return o;}
template<typename T1, typename T2>ostream& operator<<(ostream& o, const map<T1, T2>& m)
{each(p,m){o<<(p==m.begin()?"{ ":",\n  ")<<*p<<(p==--m.end()?" }":"");}return o;}
inline void _debug(){cerr<<endl;}
template<class First, class... Rest>
void _debug(const First& first, const Rest&... rest){cerr<<first<<" ";_debug(rest...);}

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;

const double PI = (1*acos(0.0)); 
const double INF = 0x3f3f3f3f;
const double INFL = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-9;
const double mod = 1e9 + 7;

inline void finput(string filename) {
    freopen(filename.c_str(), "r", stdin);
}

struct edge { int to, cap, rev; };

const int N = 100;
vector<edge> g[2*N+2];
bool used[2*N+2];

void add_edge(int u, int v, int c){
    g[u].push_back((edge){v, c, (int)g[v].size()});
    g[v].push_back((edge){u, 0, (int)g[u].size() - 1});
}

int dfs(int v, int t, int f){
    if(v == t) return f;
    used[v] = true;
    rep(i,g[v].size()){
        edge &e = g[v][i];
        if(!used[e.to] and e.cap > 0){
            int d = dfs(e.to, t, min(f, e.cap));
            if(d > 0){
                e.cap -= d;
                g[e.to][e.rev].cap += d;
                return d;
            }
        }
    }
    return 0;
}

int max_flow(int s, int t){
    int flow = 0;
    while(1){
        memset(used, 0, sizeof(used));
        int f = dfs(s, t, INF);
        if(f == 0) return flow;
        flow += f;
    }
}

int main(){
    ios_base::sync_with_stdio(0);
    // finput("./input");
    int n,x,y;
    cin >> n;

    vector<pii> ab(n);
    vector<pii> cd(n);
    rep(i,n){
        cin >> x >> y;
        ab[i] = pii(x, y);
    }
    rep(i,n){
        cin >> x >> y;
        cd[i] = pii(x, y);
    }
    rep(i,n) rep(j,n){
        if(ab[i].fi < cd[j].fi && ab[i].se < cd[j].se)
            add_edge(i, N + j, 1);
    }

    int s = 2 * N;
    int t = 2 * N + 1;
    rep(i,n) add_edge(s, i, 1);
    rep(i,n) add_edge(N + i, t, 1);

    cout << max_flow(s, t) << endl;
    return 0;
}


Compiler output:
a.cc: In function 'int max_flow(int, int)':
a.cc:92:9: error: 'memset' was not declared in this scope
   92 |         memset(used, 0, sizeof(used));
      |         ^~~~~~
a.cc:13:1: note: 'memset' is defined in header '<cstring>'; this is probably fixable by adding '#include <cstring>'
   12 | #include<cassert>
  +++ |+#include <cstring>
   13 | using namespace std;