'commit'

TangDou/Topic/HuanGenDp/CF1187E.cpp

@@ -1,49 +1,55 @@
 #include <bits/stdc++.h>
 using namespace std;
-const int N = 200010;
+const int N = 200010, M = N << 1;
 #define int long long
 #define endl "\n"
 
-vector<int> son[N];
-int vis[N], n;
+// 链式前向星
+int e[M], h[N], idx, w[M], ne[M];
+void add(int a, int b, int c = 0) {
+    e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
+}
+
+int n;
 int sz[N];
 int f[N];
-void dfs(int u) {
+void dfs(int u, int fa) {
     sz[u] = 1;
-    vis[u] = 1;
-    for (int i = 0; i < son[u].size(); i++) {
-        int v = son[u][i];
-        if (!vis[v]) {
-            dfs(v);
+
+    for (int i = h[u]; ~i; i = ne[i]) {
+        int v = e[i];
+        if (v != fa) {
+            dfs(v, u);
             sz[u] += sz[v];
         }
     }
 }
-void dp(int u) {
-    vis[u] = 1;
-    for (int i = 0; i < son[u].size(); i++) {
-        int v = son[u][i];
-        if (!vis[v]) {
+void dp(int u, int fa) {
+    for (int i = h[u]; ~i; i = ne[i]) {
+        int v = e[i];
+        if (v != fa) {
             f[v] = f[u] + sz[1] - 2 * sz[v];
-            dp(v);
+            dp(v, u);
         }
     }
 }
 
 signed main() {
+    // 初始化链式前向星
+    memset(h, -1, sizeof h);
+
     cin >> n;
     for (int i = 1; i < n; i++) {
-        int u, v;
-        cin >> u >> v;
-        son[u].push_back(v);
-        son[v].push_back(u);
+        int a, b;
+        cin >> a >> b;
+        add(a, b), add(b, a);
     }
-    dfs(1);
+
+    dfs(1, 0);
 
     for (int i = 1; i <= n; i++) f[1] += sz[i];
 
-    memset(vis, 0, sizeof(vis));
-    dp(1);
+    dp(1, 0);
 
     int ans = -0x3f;
     for (int i = 1; i <= n; i++) ans = max(ans, f[i]);