Populating Next Right Pointers in Each Node
问题描述
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
解决思路
层次遍历。
开始节点为根节点,下一层为节点的左子结点。
连接的过程中注意提前判断节点非空。
程序
public class Solution { public void connect(TreeLinkNode root) { if (root == null) { return ; } TreeLinkNode curLevel = root; while (curLevel != null) { TreeLinkNode cur = curLevel; while (cur != null) { TreeLinkNode next = cur.next; if (cur.left != null && cur.right != null) { cur.left.next = cur.right; } if (cur.right != null && next != null) { cur.right.next = next.left; } cur = next; } curLevel = curLevel.left; } } }
Follow up
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
程序
public class Solution { public void connect(TreeLinkNode root) { if (root == null) { return ; } TreeLinkNode curLevel = root; while (curLevel != null) { TreeLinkNode cur = curLevel; TreeLinkNode nextLevel = null; // mark the next node while (cur != null) { TreeLinkNode next = cur.next; while (next != null && next.left == null && next.right == null) { next = next.next; // skip node with no children } if (nextLevel == null) { // mark the first no-empty node as the next node if (cur.left != null) { nextLevel = cur.left; } else if (cur.right != null) { nextLevel = cur.right; } } if (cur.left != null && cur.right != null) { cur.left.next = cur.right; } if (next != null) { // connect cross the subtrees if (cur.right != null) { cur.right.next = next.left == null ? next.right : next.left; } else if (cur.left != null) { cur.left.next = next.left == null ? next.right : next.left; } } cur = next; } curLevel = nextLevel; } } }