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]
解题
/ \
[1, 3] [4, 6]
/ \ / \
[1, 2] [3,3] [4, 5] [6,6]
/ \ / \
[1,1] [2,2] [4,4] [5,5]
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