树的直径

题目描述

代码分析：

import java.util.*;

      class Interval {
        int start;
        int end;
      }

    public class 树的直径 {
        /**
         * 树的直径
         * @param n int整型 树的节点个数
         * @param Tree_edge Interval类一维数组 树的边
         * @param Edge_value int整型一维数组 边的权值
         * @return int整型
         */
        int res=0;
        public int solve (int n, Interval[] Tree_edge, int[] Edge_value) {
            // write code here
            ArrayList<int[]>[] map = new ArrayList[n];
            for(int i = 0; i < n; i++) map[i] = new ArrayList();
            //map添加的是key和value 树的边
            for(int i = 0; i < Tree_edge.length; i++) {
                map[Tree_edge[i].start].add(new int[] { Tree_edge[i].end, Edge_value[i] } );
                map[Tree_edge[i].end].add(new int[] { Tree_edge[i].start, Edge_value[i] } );
            }
            dfs(map, 0, new boolean[n]);
            return res;
        }

        private int dfs(ArrayList<int[]>[] map, int index, boolean[] visited) {
            visited[index] = true;
            ArrayList<int[]> list = map[index];
            int weight1 = 0, weight2 = 0;
            for(int[] child2weight: list) {
                int child = child2weight[0];
                int weight = child2weight[1];
                if(visited[child]) continue;
                int num = weight + dfs(map, child, visited);

                if(num > weight1) {
                    weight2 = weight1;
                    weight1 = num;
                } else if(num > weight2) {
                    weight2 = num;
                }
                if(weight1 + weight2 > res) res = weight1 + weight2;
            }
            return Math.max(weight1, weight2);
        }

}