CodeForces445C Civilization 带权并查集

n个点，m条边的森林，q次操作。

1、询问x所在树的直径 

2、合并x和y所在的树，使得合并后的直径最小

合并的时候贪心处理，将两集合最长路的中心连接

合并后的集合的权重为max( dis[v] , dis[u] , (dis[u]+1)/2 + (dis[v]+1)/2 + 1)  ;

import java.io.BufferedReader;import java.io.InputStream;import java.io.InputStreamReader;import java.io.PrintWriter;import java.math.BigInteger;import java.util.ArrayList;import java.util.List;import java.util.StringTokenizer;public class Main {public static void main(String[] args) {new Task().solve();}}class Task {InputReader in = new InputReader(System.in);PrintWriter out = new PrintWriter(System.out);List<Integer> adj[] ;int[] father , dis ; int maxPos , maxDep ;void dfs(int u , int fa , int dep , int root){father[u] = root ; if(maxDep < dep){maxDep = dep ;maxPos = u ;}for(int v : adj[u]){if(v == fa) continue ;dfs(v , u , dep+1 , root) ;}}int getFather(int u){if(u == father[u]) return u ;return father[u] = getFather(father[u]) ;}void solve(){int n = in.nextInt() ;int m = in.nextInt() ;int q = in.nextInt() ;adj = new List[n+1] ;for(int i = 1 ; i <= n ; i++)adj[i] = new ArrayList<Integer>() ; father = new int[n+1] ;dis = new int[n+1] ;for(int i = 1 ; i <= n ; i++) father[i] = i ; while(m -- > 0){int u = in.nextInt() ;int v = in.nextInt() ;adj[u].add(v) ;adj[v].add(u) ;u = getFather(u) ;v = getFather(v) ;if(u != v) father[u] = v ;}for(int i = 1 ; i <= n ; i++){if(father[i] == i){maxDep = 0 ; maxPos = i ;dfs(i , -1 , 0 , i) ;maxDep = 0 ;dfs(maxPos , -1 , 0 , maxPos) ;    dis[getFather(i)] = maxDep ;}}while(q-- > 0){if(in.nextInt() == 1){out.println(dis[getFather(in.nextInt())])  ;}else{int u = getFather(in.nextInt()) ;int v = getFather(in.nextInt()) ;if(u != v){father[u] = v ;dis[v] = Math.max(Math.max(dis[v] , dis[u]) , (dis[u]+1)/2 + (dis[v]+1)/2 + 1) ;}}}out.flush() ;  }}class InputReader {public BufferedReader reader;public StringTokenizer tokenizer;public InputReader(InputStream stream) {reader = new BufferedReader(new InputStreamReader(stream), 32768);tokenizer = new StringTokenizer("");}private void eat(String s) {tokenizer = new StringTokenizer(s);}public String nextLine() {try {return reader.readLine();} catch (Exception e) {return null;}}public boolean hasNext() {while (!tokenizer.hasMoreTokens()) {String s = nextLine();if (s == null)return false;eat(s);}return true;}public String next() {hasNext();return tokenizer.nextToken();}public int nextInt() {return Integer.parseInt(next());}public long nextLong() {return Long.parseLong(next());}public double nextDouble() {return Double.parseDouble(next());}public BigInteger nextBigInteger() {return new BigInteger(next());}}