Codeforces Round 1007 (Div. 2)

https://codeforces.com/contest/2071

Signed-off-by: Frederick Chen <seventeen@ohdragonboi.cn>

codeforces/Codeforces Round 1007 (Div. 2)/A_The_Play_Never_Ends.cpp

@@ -0,0 +1,28 @@
+#include <bits/stdc++.h>
+#define lo long long
+#define INF INT_MAX
+#define LLM LONG_LONG_MAX
+#define endl "\n"
+
+using namespace std;
+const int N = 1e7 + 10;
+/*
+    toothless. #17
+    @fredcss_dev
+*/
+
+int t, k;
+
+bool wczffl_503(int k) {
+    return (k % 3 == 1);
+}
+
+signed main() {
+    cin >> t;
+    while (t--){
+        cin >> k;
+        if (wczffl_503(k)) cout << "YES" << endl;
+        else cout << "NO" << endl;
+    }
+    return 0;
+}

codeforces/Codeforces Round 1007 (Div. 2)/B_Perfecto.cpp

@@ -0,0 +1,76 @@
+#include <bits/stdc++.h>
+#define lo long long
+#define INF INT_MAX
+#define LLM LONG_LONG_MAX
+#define endl "\n"
+
+using namespace std;
+const int N = 1e7 + 10;
+/*
+    toothless. #17
+    @fredcss_dev
+*/
+
+bool f(lo x) {
+    if (x < 0) return false;
+    lo root = sqrtl(x);
+    return root * root == x;
+}
+
+void wczffl_503() {
+    int n;
+    cin >> n;
+    lo total = 1LL * n * (n + 1) / 2;
+    if (f(total)) {
+        cout << "-1\n";
+        return;
+    }
+    vector<lo> s(n + 1);
+    for (int i = 1; i <= n; ++i) {
+        s[i] = (2LL * n - i + 1) * i / 2;
+    }
+    vector<bool> jhd(n + 1, false);
+    for (int i = 1; i <= n - 1; ++i) {
+        if (f(s[i])) {
+            jhd[i] = true;
+        }
+    }
+    bool bad = false;
+    for (int i = 1; i <= n; ++i) {
+        lo now = s[i];
+        if (i <= n - 1 && jhd[i]) {
+            now--;
+        }
+        if (f(now)) {
+            bad = true;
+            break;
+        }
+    }
+    if (bad) {
+        cout << "-1\n";
+        return;
+    }
+    vector<int> p(n);
+    for (int i = 0; i < n; ++i) {
+        p[i] = n - i;
+    }
+    for (int i = 1; i <= n - 1; ++i) {
+        if (jhd[i]) {
+            swap(p[i - 1], p[i]);
+        }
+    }
+    for (int x : p) {
+        cout << x << ' ';
+    }
+    cout << '\n';
+}
+
+signed main()
+{
+    int t;
+    cin >> t;
+    while (t--) {
+        wczffl_503();
+    }
+    return 0;
+}

codeforces/Codeforces Round 1007 (Div. 2)/C_Trapmigiano_Reggiano.cpp

@@ -0,0 +1,64 @@
+#include <bits/stdc++.h>
+#define lo long long
+#define INF INT_MAX
+#define LLM LONG_LONG_MAX
+#define endl "\n"
+
+using namespace std;
+const int N = 1e7 + 10;
+/*
+    toothless. #17
+    @fredcss_dev
+*/
+
+vector<int> f(int root, const vector<vector<int>>& adj) {
+    vector<int> post_order;
+    stack<tuple<int, int, bool>> s;
+    s.push({root, -1, false});
+    
+    while (!s.empty()) {
+        auto [node, parent, visited] = s.top();
+        s.pop();
+        if (visited) {
+            post_order.push_back(node);
+        } else {
+            s.push({node, parent, true});
+            for (int neighbor : adj[node]) {
+                if (neighbor != parent) {
+                    s.push({neighbor, node, false});
+                }
+            }
+        }
+    }
+    return post_order;
+}
+
+void wczffl_503() {
+    int t;
+    cin >> t;
+    while (t--) {
+        int n, st, en;
+        cin >> n >> st >> en;
+        vector<vector<int>> adj(n + 1);
+        for (int i = 0; i < n - 1; ++i) {
+            int u, v;
+            cin >> u >> v;
+            adj[u].push_back(v);
+            adj[v].push_back(u);
+        }
+        
+        vector<int> p = f(en, adj);
+        if (p.back() != en) {
+            p.push_back(en);
+        }
+        for (int x : p) {
+            cout << x << ' ';
+        }
+        cout << '\n';
+    }
+}
+
+int main() {
+    wczffl_503();
+    return 0;
+}