'commit'

TangDou/Topic/HuanGenDp/P2896.cpp

@@ -1,42 +1,46 @@
 #include <bits/stdc++.h>
 using namespace std;
-const int N = 1e5 + 100;
+const int N = 1e5 + 10, M = N << 1;
 #define int long long
 #define endl "\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 f[N], sz[N], dis[N], c[N];
-struct edge {
-    int to, w;
-};
-vector<edge> g[N];
 
 void dfs1(int u, int fa) {
     sz[u] = c[u];
-    for (int i = 0; i < g[u].size(); i++) {
-        int v = g[u][i].to;
+    for (int i = h[u]; ~i; i = ne[i]) {
+        int v = e[i];
         if (v == fa) continue;
-        dis[v] = dis[u] + g[u][i].w; // 每个点到根节点的距离
+        dis[v] = dis[u] + w[i]; // 每个点到根节点的距离
         dfs1(v, u);
         sz[u] += sz[v]; // 以u为根的子树奶牛数量
     }
 }
 void dfs2(int u, int fa) {
-    for (int i = 0; i < g[u].size(); i++) {
-        int v = g[u][i].to;
+    for (int i = h[u]; ~i; i = ne[i]) {
+        int v = e[i];
         if (v == fa) continue;
-        f[v] = f[u] + (sz[1] - 2 * sz[v]) * g[u][i].w;
+        f[v] = f[u] + (sz[1] - 2 * sz[v]) * w[i];
         dfs2(v, u);
     }
 }
 signed main() {
+    // 初始化链式前向星
+    memset(h, -1, sizeof h);
+
     int n;
     cin >> n;
     for (int i = 1; i <= n; i++) cin >> c[i];
     for (int i = 1; i < n; i++) {
-        int u, v, w;
-        cin >> u >> v >> w;
-        g[u].push_back({v, w});
-        g[v].push_back({u, w});
+        int a, b, c;
+        cin >> a >> b >> c;
+        add(a, b, c), add(b, a, c);
     }
     dfs1(1, -1);
     for (int i = 2; i <= n; i++) f[1] += dis[i] * c[i];