Populating Next Right Pointers in Each Node II

最新推荐文章于 2021-01-29 16:34:55 发布

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最新推荐文章于 2021-01-29 16:34:55 发布

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分类专栏： Leetcode

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针对Populating Next Right Pointers in Each Node问题的进阶版本，本文介绍了一种仅使用常数额外空间的方法来填充二叉树中每个节点的next指针，使同一层级的相邻节点能够相互连接。

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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,

After calling your function, the tree should look like:

         1 -> NULL
       /  \
      2 -> 3 -> NULL
     / \    \
    4-> 5 -> 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 {
    public void connect(TreeLinkNode root) {
        if (root == null) {
            return;
        }

        if (root.left != null) {
            if(root.left.next != null) {
                return;
            }
            if (root.right != null) {
                root.left.next = root.right;
            } else {
                findNextAndConnect(root.next, root.left);
            }
        }

        if (root.right != null) {
            if (root.right.next != null){
                return;
            }
            findNextAndConnect(root.next, root.right);
        }
        connect(root.next);
        connect(root.left);
        connect(root.right);
    }
    
    public void findNextAndConnect(TreeLinkNode node, TreeLinkNode toLink){
        for (; node != null; node = node.next) {
                if (node.left != null) {
                    toLink.next = node.left;
                    break;
                } else if (node.right != null) {
                    toLink.next = node.right;
                    break;
                }
        }
    }
}