populating-next-right-pointers-in-each-node

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 toNULL.

Initially, all next pointers are set toNULL.

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

//链接一个二叉树，其中不能用广度优先遍历。只能占用常量空间，网上的一种解法，记录一下。

/**
 * Definition for binary tree with next pointer.
 * struct TreeLinkNode {
 *  int val;
 *  TreeLinkNode *left, *right, *next;
 *  TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {}
 * };
 */
class Solution {
public:
    void connect(TreeLinkNode *root) {
       if(!root)     return;
       TreeLinkNode *curLev;
        
       while(root->left!=NULL){
           curLev = root;
           while(curLev != NULL){
               curLev = root;
               while(curLev != NULL){
                   curLev->left->next = curLev->right;
                   if(curLev->next!=NULL)
                           curLev->right->next = curLev->next->left;
                   curLev = curLev->next;
               }
               root = root->left;
           }
      } 
    }
};