D - Vertical Paths

https://codeforces.com/contest/1675/submission/155980007

Codeforces/1675/D/D.cpp

@@ -0,0 +1,75 @@
+#include <iostream>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2e5 + 5;
+
+int t, n, fa[N], root, ans_cnt;
+std::vector<int> g[N], ans[N];
+
+void dfs(int u, int fa, int cnt) {
+    if (g[u].size() == 1) {
+        ans[cnt].push_back(u);
+        return;
+    }
+
+    ans[cnt].push_back(u);
+
+    bool f = false;
+
+    for (int v : g[u]) {
+        if (v == fa) continue;
+
+        if (!f) {
+            dfs(v, u, cnt);
+            f = true;
+        } else {
+            dfs(v, u, ++ans_cnt);
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> t;
+
+    while (t--) {
+        root = 0;
+        ans_cnt = 1;
+
+        cin >> n;
+
+        for (int i = 1; i <= n; i++) {
+            cin >> fa[i];
+
+            if (fa[i] == i) root = i;
+
+            g[i].push_back(fa[i]);
+            g[fa[i]].push_back(i);
+        }
+
+        dfs(root, root, 1);
+
+        for (int i = 1; i <= n; i++) {
+            g[i].clear();
+        }
+
+        cout << ans_cnt << endl;
+        for (int i = 1; i <= ans_cnt; i++) {
+            cout << ans[i].size() << endl;
+            for (int x : ans[i]) {
+                cout << x << ' ';
+            }
+            cout << endl;
+
+            ans[i].clear();
+        }
+        cout << endl;
+    }
+
+    return 0;
+}