【LeetCode】117.Populating Next Right Pointers in Each Node II(Medium)解题报告

【LeetCode】117.Populating Next Right Pointers in Each Node II(Medium)解题报告

题目地址：https://leetcode.com/problems/unique-binary-search-trees/description/

题目描述：

  Follow up for problem “Populating Next Right Pointers in Each Node”.

  What if the given tree could be any binary tree? Would your previous solution still work?

  Note:You may only use constant extra space.

For example,
Given the following binary tree,
1
/  \
2    3
/ \    \
4   5    7
After calling your function, the tree should look like:
1 -> NULL
/  \
2 -> 3 -> NULL
/ \    \
4-> 5 -> 7 -> NULL

Solution:

/**
* Definition for binary tree with next pointer.
* public class TreeLinkNode {
*     int val;
*     TreeLinkNode left, right, next;
*     TreeLinkNode(int x) { val = x; }
* }
很重要
time ： O(n)
space : O(1)
*/
public class Solution {
public void connect(TreeLinkNode root) {
if(root == null) return;
TreeLinkNode head = null;
TreeLinkNode cur = root;
TreeLinkNode pre = null;
while(cur!=null){
while(cur!=null){
if(cur.left!=null){
if(pre!=null){
pre.next = cur.left;
}else head = cur.left;
pre = cur.left;
}
if(cur.right!=null){
if(pre!=null){
pre.next = cur.right;
}else head = cur.right;
pre = cur.right;
}
cur = cur.next;
}
cur = head;
pre = null;
head = null;
}
}
}

Date：2018年4月3日