'commit'

TangDou/Topic/HuanGenDp/SubTree.cpp

@@ -1,65 +1,53 @@
 #include <bits/stdc++.h>
 using namespace std;
-const int N = 1e5 + 10, M = N << 1;
+const int N = 100010;
 #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], g[N], son[N], ans[N];
-int n, mod;
-vector<int> val[N], pre[N], suc[N];
+int dp1[N], dp2[N], mod;
+int pro1[N], pro2[N];
+vector<int> edge[N];
 
 void dfs1(int u, int fa) {
-    f[u] = 1;            // 底为1，方便累乘
-    val[u].push_back(1); // 用一个动态数组，记录都是哪些数字在累乘。
-    // f[u]是累乘并取模的结果，val[u]是都是哪些数字累乘的,一个是结果，一个是过程
-    for (int i = h[u]; ~i; i = ne[i]) {
-        int v = e[i];
+    dp1[u] = 1;
+    vector<int> edgeson;
+    for (int i = 0; i < edge[u].size(); i++) {
+        int v = edge[u][i];
         if (v == fa) continue;
         dfs1(v, u);
-        son[u]++;                       // 记录u有多少个儿子,注意不是习惯的有多少个子孙节点，而是儿子有多少个
-        val[u].push_back(f[v] + 1);     // 记录过程
-        f[u] = f[u] * (f[v] + 1) % mod; // 记录结果
+        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
     }
+    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
 }
-
 void dfs2(int u, int fa) {
-    ans[u] = f[u] * g[u] % mod;
-    pre[u].resize(son[u] + 2);
-    suc[u].resize(son[u] + 2);
-    pre[u][0] = suc[u][son[u] + 1] = 1;
-
-    // 前缀积
-    for (int i = 1; i <= son[u]; i++) pre[u][i] = pre[u][i - 1] * val[u][i] % mod;
-    // 后缀积
-    for (int i = son[u]; i >= 1; i--) suc[u][i] = suc[u][i + 1] * val[u][i] % mod;
-    int m = 0;
-
-    for (int i = h[u]; ~i; i = ne[i]) {
-        int v = e[i];
-        if (v == fa) continue;
-        m++;
-        g[v] = g[u] * pre[u][m - 1] % mod * suc[u][m + 1] % mod;
-        g[v] = (g[v] + 1) % mod;
-        dfs2(v, u);
+    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);
     }
 }
-
 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;
-        add(a, b), add(b, a);
+        edge[a].push_back(b);
+        edge[b].push_back(a);
     }
-    dfs1(1, 0);
-    g[1] = 1;
-    dfs2(1, 0);
-    for (int i = 1; i <= n; i++) cout << ans[i] << endl;
+    dfs1(1, -1);
+    dfs2(1, -1);
+    for (int i = 1; i <= n; i++) cout << dp1[i] * dp2[i] % mod << endl;
 }