F - Vlad and Unfinished Business

https://codeforces.com/contest/1675/submission/156007191

Codeforces/1675/F/F.cpp

@@ -0,0 +1,58 @@
+#include <iostream>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2e5 + 5;
+
+int t, n, k, x, y, a[N], siz[N], dis[N], ans;
+std::vector<int> g[N];
+
+void dfs(int u, int fa) {
+    for (int v : g[u]) {
+        if (v == fa) continue;
+        dis[v] = dis[u] + 1;
+        dfs(v, u);
+        siz[u] += siz[v];
+        ans += !!siz[v];
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> t;
+
+    while (t--) {
+        ans = 0;
+
+        cin >> n >> k >> x >> y;
+
+        siz[y] = 1;
+
+        for (int i = 1; i <= k; i++) {
+            cin >> a[i];
+            siz[a[i]] = 1;
+        }
+
+        for (int i = 1, u, v; i < n; i++) {
+            cin >> u >> v;
+
+            g[u].push_back(v);
+            g[v].push_back(u);
+        }
+
+        dfs(x, -1);
+
+        cout << ans * 2 - dis[y] << endl;
+
+        for (int i = 1; i <= n; i++) {
+            g[i].clear();
+            dis[i] = siz[i] = 0;
+        }
+    }
+
+    return 0;
+}