首页 > 代码库 > Populating Next Right Pointers in Each Node

Populating Next Right Pointers in Each Node

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 {
    public void connect(TreeLinkNode root) {
        //利用使用一个队列
        Queue<TreeLinkNode> queue = new LinkedList<TreeLinkNode>();
        int level = 1;//记录需要出队的元素数,
        if(root == null ){
            return;
        }
        queue.offer(root);
        int count = 0;
        TreeLinkNode p = null;
        while(queue.size() > 0){
            while(count < level - 1){
                p = queue.poll();
                p.next = queue.peek();
                if(p.left != null && p.right != null){
                    queue.offer(p.left);
                    queue.offer(p.right);
                }
                count++;
            }
            p = queue.poll();
            if(p.left != null && p.right != null){
                queue.offer(p.left);
                queue.offer(p.right);
            }
            level = level * 2;
            count = 0;
        }
    }
}

题意就是将同层节点连成链,所以想到的是BFS搜索,使用一个队列存储,由于是完全二叉树,因此可以使用level来方便的控制出队的个数,从而也就处理好了层次的问题。

Runtime: 253 ms

Populating Next Right Pointers in Each Node