diff --git a/OnlineJudges/lydsy/1224.cpp b/OnlineJudges/lydsy/1224.cpp
new file mode 100644
index 0000000..5db5468
--- /dev/null
+++ b/OnlineJudges/lydsy/1224.cpp
@@ -0,0 +1,24 @@
+#include <cstdio>
+const double eps = 1e-10;
+int n, m, x, y, ans;
+double target, sum[55];
+void dfs(int pos, int cnt, double cur)
+{
+    double mx = cur + sum[pos - 1 + n - cnt] - sum[pos - 1];
+    double mn = cur + sum[m] - sum[m - (n - cnt)];
+    if (mn - target > eps || mx - target < -eps) return;
+    if (cnt == n) ans++;
+    if (cnt == n || pos == m + 1) return;
+    dfs(pos + 1, cnt, cur);
+    dfs(pos + 1, cnt + 1, cur + 1.0 / pos);
+}
+int main()
+{
+    scanf("%d%d%d%d", &n, &m, &x, &y);
+    target = 1.0 * x / y;
+    for (int i = 1; i <= m; i++)
+        sum[i] = sum[i - 1] + 1.0 / i;
+    dfs(1, 0, 0.0);
+    printf("%d", ans);
+    return 0;
+}
\ No newline at end of file
diff --git a/OnlineJudges/lydsy/2761.cpp b/OnlineJudges/lydsy/2761.cpp
new file mode 100644
index 0000000..b118220
--- /dev/null
+++ b/OnlineJudges/lydsy/2761.cpp
@@ -0,0 +1,19 @@
+#include <cstdio>
+#include <set>
+int main()
+{
+    int t, n;
+    scanf("%d", &t);
+    while (t--)
+    {
+        scanf("%d", &n);
+        std::set<int> S;
+        for (int i = 0, x; i < n; i++)
+        {
+            scanf("%d", &x);
+            if (S.count(x) == 0)
+                S.insert(x), printf(i == 0 ? "%d" : " %d", x);
+        }
+        putchar('\n');
+    }
+}
\ No newline at end of file
diff --git a/OnlineJudges/lydsy/3444.cpp b/OnlineJudges/lydsy/3444.cpp
new file mode 100644
index 0000000..13e47e7
--- /dev/null
+++ b/OnlineJudges/lydsy/3444.cpp
@@ -0,0 +1,89 @@
+#include <cstdio>
+#include <cctype>
+#include <map>
+typedef long long int64;
+const int64 mod = 989381;
+const int maxn = 500010;
+inline void readInt(int &x)
+{
+    int ch = x = 0;
+    bool F = false;
+    for (; !isdigit(ch = getchar()); F = (ch == '-'));
+    for (; isdigit(ch); ch = getchar()) x = x * 10 + ch - '0';
+    F && (x = -x);
+}
+int fa[maxn], cnt[maxn], deg[maxn], head[maxn], to[maxn << 1], next[maxn << 1], idx, n, m, num;
+bool vis[maxn];
+std::map<int, bool> M[maxn];
+int Find(int x) { return x == fa[x] ? x : fa[x] = Find(fa[x]); }
+void link(int x, int y)
+{
+    int fx = Find(x), fy = Find(y);
+    if (fx != fy)
+    {
+        fa[fx] = fy;
+        cnt[fy] += cnt[fx];
+        cnt[fx] = 0;
+    }
+}
+inline void addEdge(int x, int y)
+{
+    idx++;
+    to[idx] = y;
+    next[idx] = head[x];
+    head[x] = idx;
+}
+int fast_pow(int64 base, int pow)
+{
+    int ans = 1;
+    for (; pow; base = (base * base) % mod, pow >>= 1)
+        if (pow & 1)
+            ans = (ans * base) % mod;
+    return ans;
+}
+void dfs(int id, int f)
+{
+    num++;
+    vis[id] = true;
+    if (num > n) return;
+    for (int cur = head[id]; cur; cur = next[cur])
+        if (to[cur] != f)
+            dfs(to[cur], id);
+}
+bool check()
+{
+    for (int i = 1; i <= n; i++) if (deg[i] > 2) return false;
+    for (int i = 1; i <= n; i++)
+        if (!vis[i])
+            if (deg[i] == 1) dfs(i, 0);
+            else if (deg[i] == 0)
+                vis[i] = true, num++;
+    return num == n;
+}
+int main()
+{
+    for (int i = 0; i < maxn; i++) fa[i] = i, cnt[i] = 1;
+    readInt(n), readInt(m);
+    for (int i = 0, x, y; i < m; i++)
+    {
+        readInt(x), readInt(y);
+        if (M[x][y] || M[y][x]) continue;
+        addEdge(x, y), addEdge(y, x);
+        deg[x]++, deg[y]++;
+        link(x, y);
+        M[x][y] = M[y][x] = true;
+    }
+    int64 ans = 0;
+    if (check())
+    {
+        ans = 1;
+        int l = 0, p = 0;
+        for (int i = 1; i <= n; i++)
+            if (fa[i] == i)
+                (cnt[i] > 1 ? l : p)++;
+        for (int i = 1; i <= l + p; i++) ans = (ans * i) % mod;
+        ans = (ans * fast_pow(2, l)) % mod;
+    }
+    printf("%lld", ans);
+    return 0;
+}
\ No newline at end of file