Segment Tree Build

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.

Have you met this question in a real interview? 

Yes

Clarification

Segment Tree (a.k.a Interval Tree) is an advanced data structure which can support queries like:

• which of these intervals contain a given point
• which of these points are in a given interval

See wiki:
Segment Tree
Interval Tree

Example

Given start=0, end=3. The segment tree will be:

               [0,  3]             /        \      [0,  1]           [2, 3]      /     \           /     \   [0, 0]  [1, 1]     [2, 2]  [3, 3]

Given start=1, end=6. The segment tree will be:

               [1,  6]             /        \      [1,  3]           [4,  6]      /     \           /     \   [1, 2]  [3,3]     [4, 5]   [6,6]   /    \           /     \[1,1]   [2,2]     [4,4]   [5,5]

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.

Have you met this question in a real interview? 

Yes

Clarification

Segment Tree (a.k.a Interval Tree) is an advanced data structure which can support queries like:

• which of these intervals contain a given point
• which of these points are in a given interval

See wiki:
Segment Tree
Interval Tree

Example

Given start=0, end=3. The segment tree will be:

               [0,  3]             /        \      [0,  1]           [2, 3]      /     \           /     \   [0, 0]  [1, 1]     [2, 2]  [3, 3]

Given start=1, end=6. The segment tree will be:

               [1,  6]             /        \      [1,  3]           [4,  6]      /     \           /     \   [1, 2]  [3,3]     [4, 5]   [6,6]   /    \           /     \[1,1]   [2,2]     [4,4]   [5,5]

现在开始，要尽量少的看提示，尽量靠自己想出结果。毕竟题目是永远做不完的，一直凭靠什么并不是长久来看可以接受的方式。

这道题就是自己做的，虽然很简单。但是也希望无论简单到困难，都要一个人完整的经历一遍，要有自己的思路。而且要很清楚为什么是对的。

这道题的思路比较简单，递归构建segment tree就好，注意下右子树的start = mid+1 就好，其他的应该问题不大。

代码：

public SegmentTreeNode build(int start, int end) {        // write your code here                if(start > end) return null;        if(start == end) return new SegmentTreeNode(start, end);                int mid = (start + end)/2;        SegmentTreeNode left = build(start, mid);        SegmentTreeNode right = build(mid+1, end);        SegmentTreeNode node = new SegmentTreeNode(start, end);        node.left = left;        node.right = right;        return node;    }