线段树是一棵二叉树，他的每个节点包含了两个额外的属性start和end用于表示该节点所代表的区间。start和end都是整数，并按照如下的方式赋值:

• 根节点的 start 和 end 由 build 方法所给出。
• 对于节点 A 的左儿子，有 start=A.left, end=(A.left + A.right) / 2。
• 对于节点 A 的右儿子，有 start=(A.left + A.right) / 2 + 1, end=A.right。
• 如果 start 等于 end, 那么该节点是叶子节点，不再有左右儿子。

实现一个 build 方法，接受 start 和 end 作为参数, 然后构造一个代表区间 [start, end] 的线段树，返回这棵线段树的根

比如给定start=1, end=6，对应的线段树为：

[1,  6]             /        \      [1,  3]           [4,  6]      /     \           /     \   [1, 2]  [3,3]     [4, 5]   [6,6]   /    \           /     \[1,1]   [2,2]     [4,4]   [5,5] 解题 题目说的很细，直接根据说明做就好了 递归最简单的

/** * Definition of SegmentTreeNode: * public class SegmentTreeNode { *     public int start, end; *     public SegmentTreeNode left, right; *     public SegmentTreeNode(int start, int end) { *         this.start = start, this.end = end; *         this.left = this.right = null; *     } * } */public class Solution {    /**     *@param start, end: Denote an segment / interval     *@return: The root of Segment Tree     */    public SegmentTreeNode build(int start, int end) {        // write your code here        if(start> end)            return null;        SegmentTreeNode root = new SegmentTreeNode(start,end);        if( start == end)            return root;        root.left = build(start , (start + end)/2);        root.right = build((start + end)/2 + 1 , end);        return root;    }}

"""Definition of SegmentTreeNode:class SegmentTreeNode:    def __init__(self, start, end):        self.start, self.end = start, end        self.left, self.right = None, None"""class Solution:        # @param start, end: Denote an segment / interval    # @return: The root of Segment Tree    def build(self, start, end):        # write your code here        if start > end:            return None        root = SegmentTreeNode(start,end)        if start == end:            return root        root.left = self.build(start,( start + end)/2)        root.right = self.build(( start + end)/2  + 1,end)                return root