剑指Offer打卡day38 —— AcWing 43. 不分行从上往下打印二叉树

Posted 2021-05-21 Johnny*

【题目描述】

AcWing 43. 不分行从上往下打印二叉树

【思路】
BFS

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<Integer> printFromTopToBottom(TreeNode root) {
        
        Queue<TreeNode> q = new LinkedList<>();
        List<Integer> ans = new ArrayList<>();
        if( root == null ) return ans;
        q.offer(root);
        
        while( !q.isEmpty() ){
            TreeNode node = q.poll();
            ans.add(node.val);
            if(node.left!=null) q.offer(node.left); 
            if(node.right!=null) q.offer(node.right);
        }
        return ans;
        
    }
}