hdu 4514 湫湫系列故事――设计风景线（求树的直径）

  1 #pragma comment(linker, "/STACK:1024000000,1024000000")
  2 #include <cstdio>
  3 #include <string>
  4 #include <cstdlib>
  5 #include <cmath>
  6 #include <iostream>
  7 #include <cstring>
  8 #include <set>
  9 #include <queue>
 10 #include <algorithm>
 11 #include <vector>
 12 #include <map>
 13 #include <cctype>
 14 #include <cmath>
 15 #include <stack>
 16 //#include <tr1/unordered_map>
 17 #define freopenr freopen("in.txt", "r", stdin)
 18 #define freopenw freopen("out.txt", "w", stdout)
 19 using namespace std;
 20 //using namespace std :: tr1;
 21  
 22 typedef long long LL;
 23 typedef pair<int, int> P;
 24 const int INF = 0x3f3f3f3f;
 25 const double inf = 0x3f3f3f3f3f3f;
 26 const LL LNF = 0x3f3f3f3f3f3f;
 27 const double PI = acos(-1.0);
 28 const double eps = 1e-8;
 29 const int maxn = 1e5 + 5;
 30 const LL mod = 10000000000007;
 31 const int N = 1e6 + 5;
 32 const int dr[] = {-1, 0, 1, 0, 1, 1, -1, -1};
 33 const int dc[] = {0, 1, 0, -1, 1, -1, 1, -1};
 34 const char *Hex[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};
 35 inline LL gcd(LL a, LL b){  return b == 0 ? a : gcd(b, a%b); }
 36 int n, m;
 37 const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
 38 const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
 39 inline int Min(int a, int b){ return a < b ? a : b; }
 40 inline int Max(int a, int b){ return a > b ? a : b; }
 41 inline LL Min(LL a, LL b){ return a < b ? a : b; }
 42 inline LL Max(LL a, LL b){ return a > b ? a : b; }
 43 inline bool is_in(int r, int c){
 44     return r >= 0 && r < n && c >= 0 && c < m;
 45 }
 46 vector<P> G[maxn];
 47 int p[maxn], dp[maxn];
 48 bool vis[maxn], viss[maxn];
 49  
 50 int Find(int x){ return x == p[x] ? x : p[x] = Find(p[x]);  }
 51  
 52 int bfs(int root){
 53     memset(vis, false, sizeof vis);
 54     memset(dp, 0, sizeof dp);
 55     queue<int> q;
 56     q.push(root);
 57     vis[root] = viss[root] = true;
 58     int ans = root, maxx = 0;
 59  
 60     while(!q.empty()){
 61         int u = q.front();  q.pop();
 62         for(int i = 0; i < G[u].size(); ++i){
 63             P p = G[u][i];
 64             int v = p.first;
 65             int w = p.second;
 66             if(vis[v])  continue;
 67             vis[v] = viss[v] = true;
 68             dp[v] = dp[u] + w;
 69             if(maxx < dp[v]){
 70                 maxx = dp[v];
 71                 ans = v;
 72             }
 73             q.push(v);
 74         }
 75     }
 76     return ans;
 77 }
 78  
 79 int solve(int root){
 80     int u = bfs(root);
 81     int v = bfs(u);
 82     return dp[v];
 83 }
 84  
 85 int main(){
 86     while(scanf("%d %d", &n, &m) == 2){
 87         int u, v, c;
 88         for(int i = 1; i <= n; ++i)  G[i].clear(), p[i] = i;
 89         bool ok = false;
 90         for(int i = 0; i < m; ++i){
 91             scanf("%d %d %d", &u, &v, &c);
 92             int x = Find(u);
 93             int y = Find(v);
 94             if(x != y)  p[y] = x;
 95             else ok = true;
 96             G[u].push_back(P(v, c));
 97             G[v].push_back(P(u, c));
 98         }
 99         if(ok){  puts("YES");  continue; }
100  
101         memset(viss, false, sizeof viss);
102         int ans = 0;
103         for(int i = 1; i <= n; ++i)
104             if(!viss[i])  ans = Max(ans , solve(i));
105         printf("%d\n", ans);
106     }
107     return 0;
108 }

 1 #pragma comment(linker, "/STACK:1024000000,1024000000")
 2 #include<iostream>
 3 #include<cstdio>
 4 #include<cstring>
 5 #include<string>
 6 #include<cmath>
 7 #include<cstdlib>
 8 #include<algorithm>
 9 #include<vector>
10 using namespace std;
11 struct node
12 {
13     int v,w;
14     node(int _v, int _w) : v(_v), w(_w) {}
15 };
16 vector<node> e[100001];
17 int n,m,fa[100001],dp[100001],ans;
18 int find(int x)
19 {
20     if(x!=fa[x])
21         fa[x]=find(fa[x]);
22     return fa[x];
23 }
24 void dfs(int u,int father)
25 {
26     int maxx=0;
27     for(int i=0;i<e[u].size();i++)
28     {
29         int v=e[u][i].v;
30         int w=e[u][i].w;
31         if(v==father)
32             continue;
33         dfs(v,u);
34         ans=max(ans,dp[v]+maxx+w);
35         maxx=max(maxx,dp[v]+w);
36     }
37     dp[u]=maxx;
38 }
39 void slove()
40 {
41     for(int i=1;i<=n;i++)
42     {
43         if(dp[i]==-1)
44             dfs(i,-1);
45     }
46     printf("%d\n",ans);
47 }
48 int main()
49 {
50     while(scanf("%d%d",&n,&m)!=EOF)
51     {
52         bool flag=false;
53         ans=0;
54         for(int i=1;i<=n;i++)
55             fa[i]=i,dp[i]=-1,e[i].clear();
56         for(int i=1;i<=m;i++)
57         {
58             int x,y,z;
59             scanf("%d%d%d",&x,&y,&z);
60             e[x].push_back(node(y,z));
61             e[y].push_back(node(x,z));
62             if(flag)
63                 continue;
64             int fx,fy;
65             fx=find(x),fy=find(y);
66             if(fx!=fy)
67             {
68                 fa[fx]=fy;
69             }
70             else
71             {
72                 flag=true;
73                 continue;
74             }
75         }
76         if(flag)
77         {
78             printf("YES\n");
79             continue;
80         }
81         slove();
82     }
83     return 0;
84 }