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

註意點： 根節點用root表示

　　　　把start == end的判斷和後面代碼合並，可以少一次return

1  public SegmentTreeNode build(int start, int end) {
2      if(start == end) return new SegmentTreeNode(start, end);
3      if(start > end) return null;
4      SegmentTreeNode st = new SegmentTreeNode(start, end);
 
5      int left = start, right = (start + end) / 2;
6      st.left = build(left, right);
7      st.right = build(right + 1, end);
8      return st; 
9  }

 1 public SegmentTreeNode build(int start, int end) {
 2         // write your code here
 3         if (start > end) {
 4             return
 
 null;
 5         }
 6         SegmentTreeNode root = new SegmentTreeNode(start, end);
 7         if(start != end) {
 8            int mid = (start + end) / 2;
 9            root.left = build(start, mid);
10            root.right = build(mid + 1, end);
11         }
12         return root;
13     }

線段樹的構造