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. * public class TreeLinkNode { * int val; * TreeLinkNode left, right, next; * TreeLinkNode(int x) { val = x; } * } */ public class Solution { /**To solve this problem, we use a queue to save the nodes in the same level.<br> * * @param root -- The root node of the input tree. * @author Averill Zheng * @version 2014-06-03 * @since JDK 1.7 */ public void connect(TreeLinkNode root) { if(root != null){ Queue<TreeLinkNode> node = new LinkedList<TreeLinkNode>(); node.add(root); Queue<TreeLinkNode> nextLevel = new LinkedList<TreeLinkNode>(); while(node.peek() != null){ TreeLinkNode first = node.poll(); if(first.left != null) nextLevel.add(first.left); if(first.right != null) nextLevel.add(first.right); while(node.peek() != null){ TreeLinkNode aNode = node.poll(); if(aNode.left != null) nextLevel.add(aNode.left); if(aNode.right != null) nextLevel.add(aNode.right); first.next = aNode; first = first.next; } first.next = null; node = nextLevel; nextLevel = new LinkedList<TreeLinkNode>(); } } } }
The following code uses constant extra memory
public class Solution { public void connect(TreeLinkNode root) { if(root != null){ root.next = null; TreeLinkNode topLevel = root; TreeLinkNode nextLevelHead = null; TreeLinkNode node = null; while(topLevel != null){ if(topLevel.left != null){ nextLevelHead = topLevel.left; node = nextLevelHead; node.next = topLevel.right; node = node.next; } topLevel = topLevel.next; while(topLevel != null){ if(topLevel.left != null && node != null){ node.next = topLevel.left; node = node.next; node.next = topLevel.right; node = node.next; } topLevel = topLevel.next; } if(node != null){ node.next = null; node = node.next; } topLevel = nextLevelHead; nextLevelHead = null; } } } }