Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của ladpro98

#include <map>
#include <iostream>
#include <algorithm>
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define II pair<int, int>
#define X first
#define Y second
const int N = 100005;
using namespace std;
map<int, int> F[2];
II a[N];
int n, x, y, ans, F0, F1;

int main() {
    ios :: sync_with_stdio(0); cin.tie(0);
    cin >> n;
    FOR(i, 0, n) cin >> a[i].X >> a[i].Y;
    sort(a, a + n);
    FOR(i, 0, n) {
        F0 = F[0][a[i].X] + 1; F1 = F[1][a[i].Y] + 1;
        F[0][a[i].Y] = max(F[0][a[i].Y], F0);
        F[1][a[i].X] = max(F[1][a[i].X], F1);
        ans = max(ans, max(F0, F1));
    }
    cout << ans;
    return 0;
}

Code mẫu của RR

#include <set>
#include <map>
#include <list>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <iomanip>
#include <complex>
#include <iostream>
#include <algorithm>

#include <ctime>
#include <deque>
#include <bitset>
#include <cctype>
#include <utility>
#include <cassert>
using namespace std;

#define FOR(i,a,b) for(int i=(a),_b=(b); i<=_b; i++)
#define FORD(i,a,b) for(int i=(a),_b=(b); i>=_b; i--)
#define REP(i,a) for(int i=0,_a=(a); i<_a; i++)
#define EACH(it,a) for(__typeof(a.begin()) it = a.begin(); it != a.end(); ++it)
#define SZ(S) ((int) ((S).size()))

#define DEBUG(x) { cout << #x << " = " << x << endl; }
#define PR(a,n) { cout << #a << " = "; FOR(_,1,n) cout << a[_] << ' '; cout << endl; }
#define PR0(a,n) { cout << #a << " = "; REP(_,n) cout << a[_] << ' '; cout << endl; }

int n;
pair<int,int> a[100111];
map<int,int> f;

int main() {
    ios :: sync_with_stdio(false); cin.tie(NULL);
    cout << (fixed) << setprecision(6);
    while (cin >> n) {
        FOR(i,1,n) cin >> a[i].first >> a[i].second;
        sort(a+1, a+n+1);
        f.clear();

        int res = 0;
        FOR(i,1,n) {
            int cur = f[a[i].first] + 1;
            f[a[i].second] = max(f[a[i].second], cur);
            res = max(res, cur);
        }
        cout << res << endl;
    }
    return 0;
}

Code mẫu của hieult

#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define Fit(i,c) for (__typeof__((c).begin()) i = (c).begin(); i != (c).end(); i++)
#define inf 1000000005
#define all(a) (a).begin(), (a).end()
#define ms(a,x) memset(a, x, sizeof(a))
//#define mod 175781251
#define sz(a) ((int)(a).size())

template<class T> int getbit(T s, int i) { return (s >> i) & 1; }
template<class T> T onbit(T s, int i) { return s | (T(1) << i); }
template<class T> T offbit(T s, int i) { return s & (~(T(1) << i)); }
template<class T> int cntbit(T s) { return __builtin_popcountll(s);}
#define Rep(i,n) for(int i = 0; i < (n); ++i)
#define Repd(i,n) for(int i = (n)-1; i >= 0; --i)
#define For(i,a,b) for(int i = (a); i <= (b); ++i)
#define Ford(i,a,b) for(int i = (a); i >= (b); --i)

typedef unsigned long long ull;
typedef long long ll;
typedef double ld;
#define eps 1e-9
typedef pair<int, int> II;
template<class T> T gcd(T a, T b){ T r; while (b != 0) { r = a % b; a = b; b = r; } return a;}
template<class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
#define PI 2 * acos(0)

#define maxn 200005

int n;
vector<int> V;
int a[maxn], b[maxn], f[maxn];
II P[maxn];

int main()
{
//    freopen("jingles.in", "r", stdin);
//    freopen("jingles.out", "w", stdout);
//    freopen("in.txt", "r", stdin);
//   freopen("out.txt", "w", stdout);
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    ms(f, 0);
    cin >> n;
    For(i, 1, n){
        cin >> a[i] >> b[i];
        V.pb(a[i]); V.pb(b[i]);
    }

    sort(all(V));
    For(i, 1, n){
        a[i] = lower_bound(all(V), a[i]) - V.begin() + 1;
        b[i] = lower_bound(all(V), b[i]) - V.begin() + 1;
        P[i] = mp(a[i], b[i]);
    }

    sort(P + 1, P + n + 1);
    int res = 0;
    Ford(i, n, 1){
        f[P[i].fi] = max(f[P[i].fi], f[P[i].se] + 1);
        res = max(res, f[P[i].fi]);
    }

    cout << res << endl;

    return 0;
}

Code mẫu của skyvn97

#include<algorithm>
#include<cstdio>
#include<vector>
#define MAX   200200
#define FOR(i,a,b) for (int i=(a),_b=(b);i<=_b;i=i+1)
#define REP(i,n) for (int i=0,_n=(n);i<_n;i=i+1)
#define fi   first
#define se   second
using namespace std;
pair<int,int> a[MAX];
int cntSame[MAX],maxLen[MAX];
vector<int> haveNext[MAX];
vector<int> val;
int n,nVal;
void maximize(int &x,const int &y) {
    if (x<y) x=y;
}
void init(void) {
    scanf("%d",&n);
    FOR(i,1,n) scanf("%d%d",&a[i].fi,&a[i].se);
}
void process(void) {
    FOR(i,1,n) {
        val.push_back(a[i].fi);
        val.push_back(a[i].se);
    }
    sort(val.begin(),val.end());
    val.resize(unique(val.begin(),val.end())-val.begin());
    nVal=val.size();
    FOR(i,1,n) {
        a[i].fi=lower_bound(val.begin(),val.end(),a[i].fi)-val.begin()+1;
        a[i].se=lower_bound(val.begin(),val.end(),a[i].se)-val.begin()+1;
    }
    FOR(i,1,n) {
        if (a[i].fi==a[i].se) cntSame[a[i].fi]++;
        else haveNext[a[i].fi].push_back(a[i].se);
        maxLen[a[i].se]=1;
    }
    FOR(i,1,nVal) if (maxLen[i]>0) {
        maxLen[i]+=cntSame[i];
        REP(j,haveNext[i].size()) maximize(maxLen[haveNext[i][j]],maxLen[i]+1);
    }
    int res=0;
    FOR(i,1,nVal) maximize(res,maxLen[i]);
    printf("%d\n",res);
}
int main(void) {
    init();
    process();
    return 0;
}