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cses/introductory-problems/creating-strings.cc

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+#include <bits/stdc++.h>  // {{{
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+template <typename T>
+constexpr T MIN = std::numeric_limits<T>::min();
+
+template <typename T>
+constexpr T MAX = std::numeric_limits<T>::max();
+
+template <typename T>
+[[nodiscard]] static T sc(auto&& x) {
+  return static_cast<T>(x);
+}
+
+template <typename T>
+[[nodiscard]] static T sz(auto&& x) {
+  return static_cast<T>(x.size());
+}
+
+using ll = long long;
+using ld = long double;
+template <typename T>
+using vec = std::vector<T>;
+template <typename T, size_t N>
+using arr = std::array<T, N>;
+
+#define ff first
+#define ss second
+#define eb emplace_back
+#define pb push_back
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+//  }}}
+
+void backtrack(vec<int>& freq, string& cur, vector<string>& ans, int len) {
+  if (sz<int>(cur) == len) {
+    ans.eb(cur);
+    return;
+  }
+  for (int i = 0; i < sz<int>(freq); ++i) {
+    if (freq[i] == 0)
+      continue;
+
+    --freq[i];
+
+    cur.push_back(i + 'a');
+    backtrack(freq, cur, ans, len);
+    cur.pop_back();
+
+    ++freq[i];
+  }
+}
+
+void solve() {
+  string s;
+  cin >> s;
+
+  vec<int> m(26, 0);
+  int len = s.size();
+  for (auto c : s)
+    ++m[c - 'a'];
+
+  string cur = "";
+  vec<string> ans;
+  backtrack(m, cur, ans, len);
+  cout << ans.size() << endl;
+  for (auto& S : ans) {
+    cout << S << endl;
+  }
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+
+  solve();
+
+  return 0;
+}
+// }}}