From 4c48760d70f42b207fb52a5d3a7c2246cb5d004a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E9=BB=84=E6=B5=B7?= <10402852@qq.com>
Date: Tue, 16 Jan 2024 15:07:58 +0800
Subject: [PATCH] 'commit'

---
 TangDou/Topic/HuanGenDp/P6419.cpp | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/TangDou/Topic/HuanGenDp/P6419.cpp b/TangDou/Topic/HuanGenDp/P6419.cpp
index 8c8ec74..ed71ba8 100644
--- a/TangDou/Topic/HuanGenDp/P6419.cpp
+++ b/TangDou/Topic/HuanGenDp/P6419.cpp
@@ -11,8 +11,10 @@ void add(int a, int b, int c = 0) {
     e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
 }
 
-int sz[N]; // 哪个点上有人
-int len[N], id[N], slen[N];
+int sz[N];   // 哪个点上有人
+int len[N];  // len[u]:经过u的最长链
+int id[N];   // id[u]:最长链的第一节点
+int slen[N]; // slen[u]:经过u的次长链
 int f[N], g[N];
 
 void dfs1(int u, int fa) {
@@ -29,11 +31,17 @@ void dfs1(int u, int fa) {
         // ②  所有子节点都对u有贡献，所以f[u]+
         // ③  跑完v为根的子树后，v子树的贡献要累加到u子树上，所以f[u]+=f[v]+2*w[i]
         f[u] += f[v] + 2 * w[i];
-        int now = len[v] + w[i];
-        if (now >= len[u])
-            slen[u] = len[u], len[u] = now, id[u] = v;
-        else if (now > slen[u])
-            slen[u] = now;
+
+        // len[v]:v点出发的最长链长度
+        int x = len[v] + w[i];
+
+        // 更新最长链
+        if (x >= len[u])
+            slen[u] = len[u], len[u] = x, id[u] = v;
+        else if (x > slen[u]) // 更新次长链
+            slen[u] = x;
+
+        // 记录累计人数
         sz[u] += sz[v];
     }
 }