The structure of Segment Tree is a binary tree which each node has two attributes
start
and end
denote an segment / interval.
start and end are both integers, they should be assigned in following rules:
- The root's start and end is given by
build
method. - The left child of node A has
start=A.left, end=(A.left + A.right) / 2
. - The right child of node A has
start=(A.left + A.right) / 2 + 1, end=A.right
. - if start equals to end, there will be no children for this node.
Implement a
build
method with two parameters start and end, so that we can create a corresponding segment tree with every node has the correct start and end value, return the root of this segment tree.
Example
Given
start=0, end=3
. The segment tree will be: [0, 3]
/ \
[0, 1] [2, 3]
/ \ / \
[0, 0] [1, 1] [2, 2] [3, 3]
Given
start=1, end=6
. The segment tree will be: [1, 6]
/ \
[1, 3] [4, 6]
/ \ / \
[1, 2] [3,3] [4, 5] [6,6]
/ \ / \
[1,1] [2,2] [4,4] [5,5]
Clarification
Code (Java):
Segment Tree (a.k.a Interval Tree) is an advanced data structure which can support queries like:
- which of these intervals contain a given point
- which of these points are in a given interval
Code (Java):
/** * 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; } if (start == end) { SegmentTreeNode node = new SegmentTreeNode(start, end); return node; } int mid = start + (end - start) / 2; SegmentTreeNode root = new SegmentTreeNode(start, end); root.left = build(start, mid); root.right = build(mid + 1, end); return root; } }
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