Segment Tree Build(线段树的构造)

http://www.lintcode.com/en/problem/segment-tree-build/

/**
 * 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: start value.
     * @param end: end value.
     * @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) {
            int mid = (start + end) / 2;
            root.left = build(start, mid);
            root.right = build(mid + 1, end);
        }
        return root;
    }
};