判断是否是完全二叉树

958. Check Completeness of a Binary Tree

Medium

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Given a binary tree, determine if it is a complete binary tree.

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.

 

Example 1:

Input: [1,2,3,4,5,6] Output: true Explanation: Every level before the last is full (ie. levels with node-values {1} and {2, 3}), and all nodes in the last level ({4, 5, 6}) are as far left as possible.

Example 2:

Input: [1,2,3,4,5,null,7] Output: false Explanation: The node with value 7 isn't as far left as possible.

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isCompleteTree(TreeNode* root) {
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()){
            TreeNode* tmp = q.front();
            q.pop();
            if(tmp == NULL){
                break;
            }
            q.push(tmp->left);
            q.push(tmp->right);
        }
        while(!q.empty()){
            TreeNode* tmp = q.front();
            q.pop();
            if(tmp != NULL){
                return false;
            }
        }
        return true;
    }
};