'commit'

TangDou/Topic/HuanGenDp/SubTree.cpp

@@ -1,53 +1,66 @@
 #include <bits/stdc++.h>
 using namespace std;
-const int N = 100010;
+const int N = 100010, M = N << 1;
 #define int long long
 #define endl "\n"
-int dp1[N], dp2[N], mod;
-int pro1[N], pro2[N];
-vector<int> edge[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], g[N], mod;
+int pre[N], suff[N];
 
 void dfs1(int u, int fa) {
-    dp1[u] = 1;
-    vector<int> edgeson;
-    for (int i = 0; i < edge[u].size(); i++) {
-        int v = edge[u][i];
+    f[u] = 1;
+    vector<int> son;
+    for (int i = h[u]; ~i; i = ne[i]) {
+        int v = e[i];
         if (v == fa) continue;
         dfs1(v, u);
-        dp1[u] = dp1[u] * (dp1[v] + 1) % mod;
-        edgeson.push_back(v); // 将子节点加入集合，方便之后操作
+        f[u] = f[u] * (f[v] + 1) % mod;
+        son.push_back(v); // 将子节点加入集合，方便之后操作
     }
     int pre1 = 1;
     int pre2 = 1;
-    for (int i = 0; i < edgeson.size(); i++) {
-        pro1[edgeson[i]] = pre1;
-        pre1 = pre1 * (dp1[edgeson[i]] + 1) % mod;
-    } // 预处理前缀积
-    for (int i = edgeson.size() - 1; i >= 0; i--) {
-        pro2[edgeson[i]] = pre2;
-        pre2 = pre2 * (dp1[edgeson[i]] + 1) % mod;
-    } // 预处理后缀积
+
+    // 预处理前缀积
+    for (int i = 0; i < son.size(); i++) {
+        pre[son[i]] = pre1;
+        pre1 = pre1 * (f[son[i]] + 1) % mod;
+    }
+
+    // 预处理后缀积
+    for (int i = son.size() - 1; i >= 0; i--) {
+        suff[son[i]] = pre2;
+        pre2 = pre2 * (f[son[i]] + 1) % mod;
+    }
 }
+
 void dfs2(int u, int fa) {
-    if (fa == -1)
-        dp2[u] = 1; // 特判根节点
-    else
-        dp2[u] = (dp2[fa] * (pro1[u] * pro2[u] % mod) % mod + 1) % mod;
-    for (int i = 0; i < edge[u].size(); i++) {
-        if (edge[u][i] == fa) continue;
-        dfs2(edge[u][i], u);
+    g[u] = (g[fa] * (pre[u] * suff[u] % mod) % mod + 1) % mod;
+    for (int i = h[u]; ~i; i = ne[i]) {
+        int v = e[i];
+        if (v == fa) continue;
+        dfs2(v, u);
     }
 }
+
 signed main() {
+    // 初始化链式前向星
+    memset(h, -1, sizeof h);
+
     int n;
     cin >> n >> mod;
     for (int i = 1; i < n; i++) {
         int a, b;
         cin >> a >> b;
-        edge[a].push_back(b);
-        edge[b].push_back(a);
+        add(a, b), add(b, a);
     }
     dfs1(1, -1);
+    g[1] = 1;
     dfs2(1, -1);
-    for (int i = 1; i <= n; i++) cout << dp1[i] * dp2[i] % mod << endl;
+    for (int i = 1; i <= n; i++) cout << f[i] * g[i] % mod << endl;
 }