lght oj 1257 - Farthest Nodes in a Tree (II) (树dp)

题目链接：http://www.lightoj.com/volume_showproblem.php?problem=1257

跟hdu2196一样，两次dfs

 //#pragma comment(linker, "/STACK:102400000, 102400000")
 #include <algorithm>
 #include <iostream>
 #include <cstdlib>
 #include <cstring>
 #include <cstdio>
 #include <vector>
 #include <cmath>
 #include <ctime>
 #include <list>
 #include <set>
 #include <map>
 using namespace std;
 typedef long long LL;
 typedef pair <int, int> P;
 const int N = 1e5 + ;
 struct Edge {
     int next, to, cost;
 }edge[N << ];
 int head[N], tot;
 P d[N], pos[N];
 int up[N];

 void init(int n) {
     memset(head, -, sizeof(head));
     tot = ;
     for(int i = ; i <= n; ++i) {
         d[i].first = d[i].second = ;
         pos[i].first = pos[i].second = -;
         up[i] = ;
     }
 }

 inline void add(int u, int v, int cost) {
     edge[tot].next = head[u];
     edge[tot].to = v;
     edge[tot].cost = cost;
     head[u] = tot++;
 }

 void dfs1(int u, int p) {
     for(int i = head[u]; ~i; i = edge[i].next) {
         int v = edge[i].to;
         if(v == p)
             continue;
         dfs1(v, u);
         if(d[v].first + edge[i].cost > d[u].first) {
             if(d[u].first != )
                 d[u].second = d[u].first;
             d[u].first = d[v].first + edge[i].cost;
             pos[u].first = v;
         } else if(d[v].first + edge[i].cost > d[u].second) {
             d[u].second = d[v].first + edge[i].cost;
             pos[u].second = v;
         }
     }
 }

 void dfs2(int u, int p) {
     for(int i = head[u]; ~i; i = edge[i].next) {
         int v = edge[i].to;
         if(v == p)
             continue;
         if(v == pos[u].first) {
             up[v] = max(up[u], d[u].second) + edge[i].cost;
         } else {
             up[v] = max(up[u], d[u].first) + edge[i].cost;
         }
         dfs2(v, u);
     }
 }

 int main()
 {
     int t, n;
     scanf("%d", &t);
     for(int ca = ; ca <= t; ++ca) {
         scanf("%d", &n);
         init(n);
         int u, v, cost;
         for(int i = ; i < n; ++i) {
             scanf("%d %d %d", &u, &v, &cost);
             add(u, v, cost);
             add(v, u, cost);
         }
         dfs1(, -);
         dfs2(, -);
         printf("Case %d:\n", ca);
         for(int i = ; i < n; ++i) {
             printf("%d\n", max(d[i].first, up[i]));
         }
     }
     return ;
 }