[LeetCode]117. Populating Next Right Pointers in Each Node II

最新推荐文章于 2023-11-09 13:05:39 发布

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针对任意二叉树，实现常数额外空间填充每个节点的下一个指针，介绍一种层次遍历算法，确保每一层的相邻节点正确连接。

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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

采用层次遍历的方法，对每一层进行操作，同时在操作该层时记下下一层节点的数目

/**
 * 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;
        int thislevel = 1;
        int nextlevel = 0;
        LinkedList<TreeLinkNode> q = new LinkedList<TreeLinkNode>();
        q.add(root);
        while(q.isEmpty() == false) {
            while(thislevel > 0) {
                TreeLinkNode temp = q.poll();
                thislevel--;
                if (thislevel == 0) temp.next = null;
                else temp.next = q.peek();
                if(temp.left != null) {
                    nextlevel++;
                    q.offer(temp.left);
                }
                if(temp.right != null) {
                    nextlevel++;
                    q.offer(temp.right);
                }
            }
            thislevel = nextlevel;
            nextlevel = 0;
        }
    }
}