/* 09/12/2015
* partition the interval to two, first interval length is input argument: len,
* second one is the rest part, extra last one
*
* this partition is customized for post order traversal array.
* 09/13/2015
* add one more note to help:
* Post order traversal array: Left subtree, right subtree, Root node
* so partition them to add left subtree, right subtree to the list,
* only if the length of left subtree is known, then, partition can be done.
*/
public static ArrayList partitionByLength(Range r, int len)
{
ArrayList l = new ArrayList();
l.Add(new Range(r.start, r.start + len - 1));
l.Add(new Range(r.start + len, r.end - 1));
return l;
}
/*
* 09/12/2015
* partition the interval to two, one is left side of mid position, another is right side
* assume r.start <= mid <= r.end
*
* this partition applies the inorder traversal array
* 09/13/2015
* After all the code is done, and then, thought about, add this additional note to help myself training better,
* for next time to review my code.
*
* inorder traversal array: Left subtree, Root Node, Right subtree
* so, if the root node position can be identified, then two subtree can be seperated by root node.
*/
public static ArrayList partitionByMidPoint(Range r, int mid)
{
ArrayList l = new ArrayList();
l.Add(new Range(r.start, mid - 1));
l.Add(new Range(mid + 1, r.end));
return l;
}
/*
*
1
--------|-------
2 3
----|---- ----|----
4 5 6 7
preorder traversal: 1245367
inorder traversal: 4251637
postorder traversal: 4526731
*
* code reference:
* http://siddontang.gitbooks.io/leetcode-solution/content/tree/construct_binary_tree.html
*
* Julia's comment:
practice the partition methods
*
* 2. online judge:
* 202 / 202 test cases passed.
Status: Accepted
Runtime: 192 ms
*/
public static TreeNode build(int[] inorder, Range iR,
int[] postorder, Range pR)
{
if (iR.start > iR.end || pR.start > pR.end)
{
return null;
}
int lastOne = pR.end;
TreeNode root = new TreeNode(postorder[lastOne]);
int v = postorder[lastOne]; // v - root value
int p = (int)htable[v]; // p - root position in inorder traversal array
int len = p - iR.start; // count - the size of left subtree, how many nodes
ArrayList l1 = partitionByMidPoint(iR, p);
ArrayList l2 = partitionByLength(pR, len);
root.left = build(inorder, (Range)l1[0], postorder, (Range)l2[0]);
root.right = build(inorder, (Range)l1[1], postorder, (Range)l2[1]);
return root;
}