public SegmentTree build(int start, int end) {
if (start > end) {
return null;
}
SegmentTree root = new SegmentTree(start, end);
if (start == end) {
return root;
}
int mid = start + ((end - start) >> 1);
root.left = build(start, mid);
root.right = build(mid + 1, end);
return root;
}
