CSES-3403 Longest Common Subsequence

#include <bits/stdc++.h>
using namespace std;

#define pb push_back
#define fi first
#define se second
#define INF LONG_LONG_MAX/1000
#define WA() cin.tie(0)->sync_with_stdio(0)
#define all(x) (x).begin(), (x).end()
#define int long long
#define PII pair<int, int>

signed main() { WA();
    int n, m; cin >> n >> m;
    vector<int> a(n), b(m);
    for (auto &i : a) cin >> i;
    for (auto &i : b) cin >> i;
    vector<vector<int>> v(n+1, vector<int>(m+1));
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (a[i-1] == b[j-1]) v[i][j] = v[i-1][j-1]+1;
            else v[i][j] = max(v[i-1][j], v[i][j-1]);
        }
    }
    int i = n, j = m;
    vector<int> ans;
    while (i && j) {
        if (a[i-1] == b[j-1]) ans.pb(a[i-1]), i--, j--;
        else if (v[i-1][j] > v[i][j-1]) i--;
        else j--;
    }

    cout << v[n][m] << '\n';
    for (auto &i : vector<int>(ans.rbegin(), ans.rend())) cout << i << ' ';
}