C++ 解法, 执行用时: 2ms, 内存消耗: 524KB, 提交时间: 2022-02-09

/*
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};*/
class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
        vector<int> ret;
        if (!root) {
            return ret;
        }
        
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()) {
            int size = q.size();
            for (int i=0; i<size; i++) {
                TreeNode *p = q.front();
                q.pop();
                ret.push_back(p->val);
                if (p->left) {
                    q.push(p->left);
                }
                
                if (p->right) {
                    q.push(p->right);
                }
            }
        }
        return ret;
    }
};

C++ 解法, 执行用时: 2ms, 内存消耗: 544KB, 提交时间: 2022-02-10

/*
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};*/
class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
        vector<int> ret;
        if(root==nullptr)return ret;
        queue<TreeNode*> qq;
        qq.push(root);
        while(!qq.empty())
        {
            TreeNode*rt=qq.front();
            qq.pop();
            ret.push_back(rt->val);
            if(rt->left!=nullptr)
            qq.push(rt->left);
            if(rt->right!=nullptr)
            qq.push(rt->right);
            
        }
        return ret;
    }
};

C++ 解法, 执行用时: 2ms, 内存消耗: 556KB, 提交时间: 2022-02-10

/*
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};*/
class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
        queue<TreeNode*> q;
        if(root != NULL) { q.push(root); } 
        vector<int> ans;
        while(!q.empty()){
            int size = q.size();
            for(int i = 0; i < size; ++i){
                ans.push_back(q.front()->val);
                if(q.front()->left) { q.push(q.front()->left); }
                if(q.front()->right) { q.push(q.front()->right); }
                q.pop();
            }
        }
        return ans;
    }
};

C++ 解法, 执行用时: 2ms, 内存消耗: 556KB, 提交时间: 2021-11-23

/*
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};*/
class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
        vector<int> res;
        if(!root) return res;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()) {
            auto t=q.front();
            if(t->left) q.push(t->left);
            if(t->right) q.push(t->right);
            q.pop();
            res.push_back(t->val);
        }
        return res;
    }
};

C++ 解法, 执行用时: 2ms, 内存消耗: 604KB, 提交时间: 2022-03-12

/*
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};*/
class Solution {
public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
		vector<int> res;
		if (root == NULL) return res;
		queue<TreeNode*> que;
		que.push(root);
		TreeNode* node = NULL;
		while (!que.empty()) {
			node = que.front();
			res.push_back(node->val);
			que.pop();
			if (node->left != NULL) que.push(node->left);
			if (node->right != NULL) que.push(node->right);
		}
		return res;
	}
};