https://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/
http://blog.csdn.net/linhuanmars/article/details/23510601
/**
* Definition for binary tree with next pointer.
* public class TreeLinkNode {
* int val;
* TreeLinkNode left, right, next;
* TreeLinkNode(int x) { val = x; }
* }
*/
public class Solution {
public void connect(TreeLinkNode root) {
// Same as https://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node/
// But queue is not allowed
TreeLinkNode curhead = root;
TreeLinkNode nexthead = null;
TreeLinkNode pre = null; // pre in next level
// Iterate cur level, assign next level
while (curhead != null)
{
// Start to iterate current level
TreeLinkNode cur = curhead;
while (cur != null)
{
if (cur.left != null)
{
if (nexthead == null)
nexthead = cur.left;
if (pre != null)
pre.next = cur.left;
pre = cur.left;
}
if (cur.right != null)
{
// Same logic as leftnode handling.
if (nexthead == null)
nexthead = cur.right;
if (pre != null)
pre.next = cur.right;
pre = cur.right;
}
cur = cur.next;
}
// After iteration this level.
// Move to next nevel.
if (nexthead != null)
{
curhead = nexthead;
nexthead = null;
pre = null;
}
else
{
// No next head.
// We are finished.
curhead = null;
}
}
}
}