Segment Tree Build II

build之后不要忘记把当前Node和它的左右child连起来
/**
 * Definition of SegmentTreeNode:
 * public class SegmentTreeNode {
 *     public int start, end, max;
 *     public SegmentTreeNode left, right;
 *     public SegmentTreeNode(int start, int end, int max) {
 *         this.start = start;
 *         this.end = end;
 *         this.max = max
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     *@param A: a list of integer
     *@return: The root of Segment Tree
     */
    public SegmentTreeNode build(int[] A) {
        // write your code here
        return build(A, 0, A.length - 1);
    }
    private SegmentTreeNode build(int[] A, int start, int end) {
        if (start > end) return null;
        if (start == end) return new SegmentTreeNode(start, end, A[start]);
        int mid = (start + end) / 2;
        SegmentTreeNode left = build(A, start, mid);
        SegmentTreeNode right = build(A, mid + 1, end);
        SegmentTreeNode res = new SegmentTreeNode(start, end, Math.max(left.max, right.max));
        res.left = left;
        res.right = right;
        return res;
    }
}