题解 | #判断是不是完全二叉树#C++解法，仅关注最后一行

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return bool布尔型
     */
    int height(TreeNode*root)
    {
        if(root)
        {
            int m=height(root->left);
            int n=height(root->right);
            return max(m,n)+1;
        }
        return 0;
    }
    void answer(TreeNode*root,int h,vector <vector <TreeNode*>> &ans)
    {
        if(root)
        {
            ans[h].push_back(root);
            answer(root->left,h+1,ans);
            answer(root->right,h+1,ans);
        }
    }
    bool isCompleteTree(TreeNode* root) 
    {
        int i=0;
        int h=height(root);
        vector <vector <TreeNode*>> ans(h);
        answer(root,i,ans);
        if(h==0  ||  h==1)
        {
            return 1;
        }
        else 
        {
            int count=1;
            for(i=0;i<h-1;i++)
            {
                int m=ans[i].size();
                if(m!=count)
                {
                    return 0;
                }
                count*=2;
            }
            count/=2;
            int flag=0;
            for(i=0;i<count;i++)
            {
                TreeNode*t=ans[h-2][i];
                if(t->left)
                {
                    if(flag>=1)
                    {
                        return 0;
                    }
                }
                else 
                {
                    flag++;
                }
                if(t->right)
                {
                    if(flag>=1)
                    {
                        return 0;
                    }
                }
                else 
                {
                    flag++;
                }
            }
        }
        return 1;
    }
};