题意:输出从一颗树中所有结点出发可以走的最长的路。
思路:先找到树上最长链然后判断两个端点中到每个结点远的距离就是答案。
代码如下:
1 #include <stdio.h>
2 #include <string.h>
3 #include <iostream>
4 #include <algorithm>
5 #include <vector>
6 #include <queue>
7 #include <set>
8 #include <map>
9 #include <string>
10 #include <math.h>
11 #include <stdlib.h>
12 #include <time.h>
13 #define MP(a, b) make_pair(a, b)
14 #define PB(a) push_back(a)
15 using namespace std;
16
17 const int LEN = 10010;
18 const int INF = 0x3f3f3f3f;
19 typedef pair<int, int> pii;
20 vector<pii> Map[LEN];
21 int n, vis[LEN], dis[LEN], disa[LEN];
22
23
24 int bfs(int v){
25 queue<int> q;
26 memset(vis, 0, sizeof vis);
27 memset(dis, 0, sizeof dis);
28 q.push(v);
29 vis[v] = 1;
30 while(!q.empty()){
31 int nv = q.front(); q.pop();
32 for(int i=0; i<Map[nv].size(); i++){
33 int x = Map[nv][i].first;
34 if(!vis[x]){
35 vis[x] = 1;
36 dis[x] = dis[nv] + Map[nv][i].second;
37 q.push(x);
38 }
39 }
40 }
41 int maxv = -INF, maxn;
42 for(int i=0; i<n; i++){
43 if(maxv < dis[i]){
44 maxv = dis[i];
45 maxn = i;
46 }
47 }
48 return maxn;
49 }
50
51 int main()
52 {
53 // freopen("in.txt","r",stdin);
54 // freopen("out.txt","w",stdout);
55
56 int a, b;
57 while(scanf("%d", &n)!=EOF){
58 for(int i=0; i<LEN; i++) Map[i].clear();
59 for(int i=1; i<n; i++){
60 scanf("%d%d", &a, &b);
61 a--;
62 Map[i].PB(MP(a, b));
63 Map[a].PB(MP(i, b));
64 }
65 int vexa = bfs(0);
66 int vexb = bfs(vexa);
67 for(int i=0; i<n; i++)disa[i] = dis[i];
68 bfs(vexb);
69 for(int i=0; i<n; i++){
70 printf("%d\n", max(disa[i], dis[i]));
71 }
72 }
73 return 0;
74 }
hdu 2196(树的最长链),布布扣,bubuko.com
时间: 2024-10-27 14:06:52