Tree: Segment Tree Build

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 hasstart=(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.

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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

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

See wiki: Segment Tree Interval Tree

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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; } }