'commit'

TangDou/Topic/HuanGenDp/CF1324F.cpp

@@ -2,39 +2,39 @@
 using namespace std;
 const int N = 200010, M = N << 1;
 
-int n, a[N], f1[N], f2[N];
-int head[N << 1], nxt[N << 1], to[N << 1], tot = 0;
-void add(int u, int v) {
-    to[++tot] = v;
-    nxt[tot] = head[u];
-    head[u] = tot;
+// 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, a[N], f1[N], f2[N];
+
 void dfs1(int u, int fa) {
     if (a[u])
         f1[u] = 1;
     else
         f1[u] = -1;
 
-    for (int i = head[u]; i; i = nxt[i]) {
-        int v = to[i];
-        if (v == fa)
-            continue;
+    for (int i = h[u]; ~i; i = ne[i]) {
+        int v = e[i];
+        if (v == fa) continue;
         dfs1(v, u);
         f1[u] += max(f1[v], 0);
     }
 }
 
 void dfs2(int u, int fa) {
-    for (int i = head[u]; i; i = nxt[i]) {
-        int v = to[i];
-        if (v == fa)
-            continue;
+    for (int i = h[u]; ~i; i = ne[i]) {
+        int v = e[i];
+        if (v == fa) continue;
         f2[v] = max(f2[u] + f1[u] - max(f1[v], 0), 0);
         dfs2(v, u);
     }
 }
 int main() {
+    // 初始化链式前向星
+    memset(h, -1, sizeof h);
     cin >> n;
 
     for (int i = 1; i <= n; i++) cin >> a[i];