［LintCode］Segment Tree Build 构造线段树

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
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

/** * 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     */／／BFS    public SegmentTreeNode build(int start, int end) {        if(start > end) return null;        SegmentTreeNode root = new SegmentTreeNode(start, end);        Queue<SegmentTreeNode> queue = new LinkedList<SegmentTreeNode>();        if(start < end) {            queue.add(root);        }        while(!queue.isEmpty()) {            SegmentTreeNode node = queue.poll();            int start1 = node.start;            int end1 = (node.start + node.end)/2;            int start2 = end1 + 1;            int end2 = node.end;            node.left = new SegmentTreeNode(start1, end1);            node.right = new SegmentTreeNode(start2, end2);            if(start1 != end1) {                queue.add(node.left);            }            if(start2 != end2) {                queue.add(node.right);            }        }        return root;    }}