new file: 0x10/3.cpp

0x10/3.cpp

@@ -0,0 +1,37 @@
+// 129
+#include <bits/stdc++.h>
+using namespace std;
+vector<int> ans;
+int stk[25], tot, n, cnt;
+void dfs(int now)
+{
+    if (cnt >= 20)
+        return;
+    if (now > n)
+    {
+        cnt++;
+        for (auto x : ans)
+            cout << x;
+        for (int i = tot - 1; i >= 0; i--)
+            cout << stk[i];
+        puts("");
+        return;
+    }
+    if (tot)
+    {
+        ans.push_back(stk[--tot]);
+        dfs(now);
+        stk[tot++] = ans.back();
+        ans.pop_back();
+    }
+    stk[tot++] = now;
+    dfs(now + 1);
+    tot--;
+}
+
+int main()
+{
+    cin >> n;
+    dfs(1);
+    return 0;
+}