蓝桥杯 大臣的旅费 JAVA

思路:该题要使用树的直径。

求树的直径:先从一个点DFS，找到一个最远的点v，然后以该点v作为起点再次DFS，找到点t，则v到t则为该树的最远直径。

import java.util.Arrays;
import java.util.Scanner;

public class 大臣的旅费 {
    
    public static int ans = Integer.MIN_VALUE;
    public static int temp,n;
    public static boolean[] visited = new boolean[7010];
    public static int[][] map = new int[7010][7010];
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();
        sc.nextLine();
        
        for(int i=0;i<n-1;i++){
            int x = sc.nextInt()-1;
            int y = sc.nextInt()-1;
            int dis = sc.nextInt();
            
            map[x][y] = dis;
            map[y][x] = dis;
        }
        
        visited[0] = true;
        DFS(0,0);
        Arrays.fill(visited, false);
        
        visited[temp] = true;
        ans = Integer.MIN_VALUE;
        DFS(temp, 0);//第二次深度优先搜索

        //System.out.println(ans);
        int sum = (11+10+ans)*ans/2;
        System.out.println(sum);
    }
    
    
    public static void DFS(int start,int dist){//起点，距离
        if(dist>ans){
            ans = dist;
            temp = start;
        }
        for(int i=0;i<n;i++){
            if(!visited[i]&&map[start][i]>0){
                visited[i] = true;
                dist+= map[start][i];
                DFS(i, dist);
                visited[i] = false;
                dist -= map[start][i];
            }
        }
        return;
    }
}