CODE 17: Populating Next Right Pointers in Each Node

最新推荐文章于 2021-12-24 11:09:57 发布

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本文介绍了一种在完美二叉树中填充每个节点的next指针的方法，使得每个节点指向其右侧相邻节点。通过广度优先搜索实现，确保了只使用常数额外空间。

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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,

After calling your function, the tree should look like:

         1 -> NULL
       /  \
      2 -> 3 -> NULL
     / \  / \
    4->5->6->7 -> NULL

	public void connect(TreeLinkNode root) {
		// Start typing your Java solution below
		// DO NOT write main() function
		if (null == root) {
			return;
		}
		bfs(root);
	}

	private void bfs(TreeLinkNode root) {
		Queue<TreeLinkNode> queue = new LinkedList<TreeLinkNode>();
		queue.offer(root);
		int queueNumber = 1;
		int layerNumber = 0;
		TreeLinkNode tempNode = null;
		while (!queue.isEmpty()) {
			tempNode = queue.poll();
			queueNumber--;
			if (null != tempNode.left) {
				queue.offer(tempNode.left);
				layerNumber++;
			}
			if (null != tempNode.right) {
				queue.offer(tempNode.right);
				layerNumber++;
			}
			if (queueNumber != 0) {
				tempNode.next = queue.peek();
			} else {
				tempNode.next = null;
			}

			if (queueNumber == 0 && layerNumber != 0) {
				queueNumber = layerNumber;
				layerNumber = 0;
			}
		}
	}