线段树的构造

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;
    }
}
Java Code
"""
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
Python Code