leetcode| 958. Check Completeness of a Binary Tree

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本文介绍了如何解决LeetCode周赛中的第958题，涉及完全二叉树的定义及层次遍历的解题策略。完全二叉树每个层级都完全填充，最后一层的所有节点尽可能靠左。

今天参加周赛的题目：

完全二叉树的定义：

Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.
https://leetcode.com/contest/weekly-contest-115/problems/check-completeness-of-a-binary-tree/

解法：层次遍历

    public boolean isCompleteTree(TreeNode root) {
        if (root == null) return true;
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);
        int i=0;
        while (true){
            int len = q.size();
            for(;i<len;i++){
                TreeNode e = ((LinkedList<TreeNode>) q).get(i);
                if(e==null){
                    len = q.size();
                    for(;i<len;i++){
                        if(((LinkedList<TreeNode>) q).get(i)!=null) return false;
                    }
                    return true;
                }else{
                    q.offer(e.left);
                    q.offer(e.right);
                }
            }
        }
    }