A bunch new problems

Codeforces Round 921 (Div. 1)/A. Did We Get Everything Covered?.cpp

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+/* Problem URL: https://codeforces.com/problemset/problem/1924/A */
+
+#include <bits/stdc++.h>
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/tree_policy.hpp>
+
+using namespace std;
+using namespace __gnu_pbds;
+
+template <class T, class comp = less<>>
+using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;
+
+#define V vector
+
+#define rmin(a, b) a = min(a, b)
+#define rmax(a, b) a = max(a, b)
+
+#define rep(i, lim) for (int i = 0; i < (lim); i++)
+#define nrep(i, s, lim) for (int i = s; i < (lim); i++)
+
+#define repv(i, v) for (auto &i : (v))
+#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
+#define sortv(v) sort(v.begin(), v.end())
+#define all(v) (v).begin(), (v).end()
+
+using vi = vector<int>;
+using vvi = vector<vi>;
+using vvvi = vector<vvi>;
+using vvvvi = vector<vvvi>;
+
+using ll = long long;
+
+using vl = vector<ll>;
+using vvl = vector<vl>;
+using vvvl = vector<vvl>;
+using vvvvl = vector<vvvl>;
+
+template<class v>
+auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
+    os << vec[0];
+    for (size_t i = 1; i < vec.size(); i++) {
+        os << ' ' << vec[i];
+    }
+    os << '\n';
+    return os;
+}
+
+template<class v>
+auto operator>>(istream &is, vector<v> &vec)->istream& {
+    for (auto &i : vec) {
+        is >> i;
+    }
+    return is;
+}
+
+template<class v>
+auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
+    for (auto &i : vec) {
+        os << i[0];
+        for (size_t j = 1; j < i.size(); j++) {
+            os << ' ' << i[j];
+        }
+        os << '\n';
+    }
+    return os;
+}
+
+template<class v>
+auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
+    for (auto &i : vec) {
+        for (auto &j : i) {
+            is >> j;
+        }
+    }
+    return is;
+}
+
+const int oo = INT32_MAX >> 1;
+const ll OO = INT64_MAX >> 1;
+
+
+void pre()
+{
+
+}
+
+#define TEST 1
+
+void solve()
+{
+    int n, k, m;
+    cin >> n >> k >> m;
+    string a;
+    cin >> a;
+
+    vi pos(k, -1);
+    vvi ne(m + 1, vi(k, -1));
+
+    for (int i = m - 1; i >= 0; i--) {
+        ne[i + 1] = pos;
+        pos[a[i] - 'a'] = i + 1;
+    }
+    ne[0] = pos;
+
+    vi memo(m + 1, -1);
+
+    function<int(int)> dp = [&](int i) {
+        if (i == -1) {
+            return 0;
+        }
+
+        int &ans = memo[i];
+        if (ans != -1) {
+            return ans;
+        }
+
+        ans = oo;
+        rep(j, k) {
+            rmin(ans, dp(ne[i][j]) + 1);
+        }
+
+        return ans;
+    };
+
+    int c = dp(0) - 1;
+    if (c >= n) {
+        cout << "YES\n";
+        return;
+    }
+
+    cout << "NO\n";
+
+    int now = 0;
+    string ans;
+    while (ans.size() < n) {
+        int j = 0;
+        while (1) {
+            if (ne[now][j] == -1) {
+                while (ans.size() < n) {
+                    ans += j + 'a';
+                }
+                break;
+            }
+
+            if (memo[ne[now][j]] == c) {
+                c--;
+                ans += j + 'a';
+                now = ne[now][j];
+                break;
+            }
+
+            j++;
+        }
+    }
+
+    cout << ans << '\n';
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    pre();
+
+    int t;
+    (TEST && cin >> t) || (t = 1);
+    while (t--) {
+        solve();
+    }
+}