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

Posted 2020-08-13 Recoder

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

跟hdu2196一样，两次dfs

 1 //#pragma comment(linker, "/STACK:102400000, 102400000")
 2 #include <algorithm>
 3 #include <iostream>
 4 #include <cstdlib>
 5 #include <cstring>
 6 #include <cstdio>
 7 #include <vector>
 8 #include <cmath>
 9 #include <ctime>
10 #include <list>
11 #include <set>
12 #include <map>
13 using namespace std;
14 typedef long long LL;
15 typedef pair <int, int> P;
16 const int N = 1e5 + 5;
17 struct Edge {
18     int next, to, cost;
19 }edge[N << 1];
20 int head[N], tot;
21 P d[N], pos[N];
22 int up[N];
23 
24 void init(int n) {
25     memset(head, -1, sizeof(head));
26     tot = 0;
27     for(int i = 0; i <= n; ++i) {
28         d[i].first = d[i].second = 0;
29         pos[i].first = pos[i].second = -1;
30         up[i] = 0;
31     }
32 }
33 
34 inline void add(int u, int v, int cost) {
35     edge[tot].next = head[u];
36     edge[tot].to = v;
37     edge[tot].cost = cost;
38     head[u] = tot++;
39 }
40 
41 void dfs1(int u, int p) {
42     for(int i = head[u]; ~i; i = edge[i].next) {
43         int v = edge[i].to;
44         if(v == p)
45             continue;
46         dfs1(v, u);
47         if(d[v].first + edge[i].cost > d[u].first) {
48             if(d[u].first != 0)
49                 d[u].second = d[u].first;
50             d[u].first = d[v].first + edge[i].cost;
51             pos[u].first = v;
52         } else if(d[v].first + edge[i].cost > d[u].second) {
53             d[u].second = d[v].first + edge[i].cost;
54             pos[u].second = v;
55         }
56     }
57 }
58 
59 void dfs2(int u, int p) {
60     for(int i = head[u]; ~i; i = edge[i].next) {
61         int v = edge[i].to;
62         if(v == p) 
63             continue;
64         if(v == pos[u].first) {
65             up[v] = max(up[u], d[u].second) + edge[i].cost;
66         } else {
67             up[v] = max(up[u], d[u].first) + edge[i].cost;
68         }
69         dfs2(v, u);
70     }
71 }
72 
73 int main()
74 {
75     int t, n;
76     scanf("%d", &t);
77     for(int ca = 1; ca <= t; ++ca) {
78         scanf("%d", &n);
79         init(n);
80         int u, v, cost;
81         for(int i = 1; i < n; ++i) {
82             scanf("%d %d %d", &u, &v, &cost);
83             add(u, v, cost);
84             add(v, u, cost);
85         }
86         dfs1(0, -1);
87         dfs2(0, -1);
88         printf("Case %d:\n", ca);
89         for(int i = 0; i < n; ++i) {
90             printf("%d\n", max(d[i].first, up[i]));
91         }
92     }
93     return 0;
94 }