從上往下打印二叉樹

從上往下打印出二叉樹的每個節點，同層節點從左至右打印。

c++

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;ret.clear();queue<TreeNode*> q;while(!q.empty()) q.pop();if(root!=NULL)q.push(root);elsereturn ret;while(!q.empty()){TreeNode* cur=q.front();q.pop();if(cur->left!=NULL)q.push(cur->left);if(cur->right!=NULL)q.push(cur->right);ret.push_back(cur->val);}return ret;} };

Java

import java.util.*; /* class TreeNode {int val = 0;TreeNode left = null;TreeNode right = null;public TreeNode(int val) {this.val = val;}} */ public class Solution {public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {ArrayList<Integer> ans=new ArrayList();Queue<TreeNode> q=new LinkedList<TreeNode>();if(root==null)return ans;q.offer(root);while(!q.isEmpty()) {TreeNode cur=q.poll();if(cur.left!=null)q.offer(cur.left);if(cur.right!=null)q.offer(cur.right);ans.add(cur.val);}return ans;} }

總結

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