#!/usr/bin/env python
# -*- coding: utf-8 -*-
'''
*****************************************
Author:         zhlinh
Email:          zhlinhng@gmail.com
Version:        0.0.1
Created Time:   2016-03-09
Last_modify:    2016-03-09
******************************************
'''

'''
Given a binary tree

    struct TreeLinkNode {
      TreeLinkNode *left;
      TreeLinkNode *right;
      TreeLinkNode *next;
    }
Populate each next pointer to point to its next right node.
If there is no next right node, the next pointer should be set to NULL.

Initially, all next pointers are set to NULL.

Note:

You may only use constant extra space.
You may assume that it is a perfect binary tree
(ie, all leaves are at the same level, and every parent has two children).
For example,
Given the following perfect binary tree,
         1
       /  \
      2    3
     / \  / \
    4  5  6  7
After calling your function, the tree should look like:
         1 -> NULL
       /  \
      2 -> 3 -> NULL
     / \  / \
    4->5->6->7 -> NULL
'''

# Definition for binary tree with next pointer.
class TreeLinkNode(object):
   def __init__(self, x):
       self.val = x
       self.left = None
       self.right = None
       self.next = None

class Solution(object):
    def connect(self, root):
        """
        :type root: TreeLinkNode
        :rtype: nothing
        """
        if not root:
            return
        pre_head = root
        cur = None
        while pre_head.left:
            cur = pre_head 
            while cur:
                cur.left.next = cur.right
                if cur.next:
                    cur.right.next = cur.next.left
                cur = cur.next
            pre_head = pre_head.left
