[LintCode] Segment Tree Build

Question

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.

Solution

A simple top-down run through.

Code

``````/**
* 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) {