BOJ 24535 둘레길

void solve(){
    int N; cin >> N;
    vector<pii> points(N);
    vector<int> xs, ys;
    rep(i, 0, N){
        int x, y; cin >> x >> y;
        points[i] = {x, y};
        xs.push_back(x);
        ys.push_back(y);
    }
    sort(all(xs)); xs.erase(unique(all(xs)), xs.end());
    sort(all(ys)); ys.erase(unique(all(ys)), ys.end());

    rep(i, 0, N){
        points[i].first = lower_bound(all(xs), points[i].first) - xs.begin();
        points[i].second = lower_bound(all(ys), points[i].second) - ys.begin();
    }

    vector<vector<bool>> isPoint(xs.size(), vector<bool>(ys.size()));
    for(auto [x, y] : points) isPoint[x][y] = true;

    int ans = 0;
    vector<vector<int>> DP(ys.size(), vector<int>(ys.size()));
    rrep(i, 0, xs.size()){
        vector<vector<int>> cur_cnt(ys.size(), vector<int>(ys.size())); // cur_cnt[j][k] = j, k 사이에 있는 점의 개수
        rep(j, 0, ys.size()){
            if(isPoint[i][j]) cur_cnt[j][j]++;
            rep(k, j+1, ys.size()) cur_cnt[j][k] = cur_cnt[j][k-1] + isPoint[i][k];
        }

        rep(j, 0, ys.size()) rep(k, j+1, ys.size()){
            ans = max(ans, cur_cnt[j][k] + DP[j][k]);
            DP[j][k] = max(DP[j][k] + isPoint[i][j] + isPoint[i][k], cur_cnt[j][k]);
        }
    }

    // 세로 한줄 처리
    rep(i, 0, ys.size()){
        int cnt = 0;
        rep(j, 0, xs.size()) if(isPoint[j][i]) cnt++;
        ans = max(ans, cnt);
    }
    cout << ans;
}