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  • 剑指offer:面试题23、从上往下打印二叉树

    题目描述

    从上往下打印出二叉树的每个节点,同层节点从左至右打印。

    代码示例

    import java.util.ArrayList;
    import java.util.LinkedList;
    import java.util.List;
    import java.util.Queue;
    
    public class Offer23 {
        public static void main(String[] args) {
            TreeNode root = new TreeNode(1);
            root.left = new TreeNode(2);
            root.right = new TreeNode(3);
            root.left.left = new TreeNode(4);
            root.left.right = new TreeNode(5);
            Offer23 testObj = new Offer23();
            System.out.println(testObj.printFromTopToBottom(root));
        }
    
        static class TreeNode {
            int val;
            TreeNode left;
            TreeNode right;
            TreeNode(int val) {
                this.val = val;
            }
        }
    
        public List<Integer> printFromTopToBottom(TreeNode root) {
            Queue<TreeNode> queue = new LinkedList<>();
            List<Integer> res = new ArrayList<>();
            queue.add(root);
            while (!queue.isEmpty()) {
                int count = queue.size();
                for (int i = 0; i < count; i++) {
                    TreeNode node = queue.poll();
                    res.add(node.val);
                    if (node.left != null) {
                        queue.offer(node.left);
                    }
    
                    if (node.right != null) {
                        queue.offer(node.right);
                    }
                }
            }
            return res;
        }
    }
    
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  • 原文地址:https://www.cnblogs.com/ITxiaolei/p/13167025.html
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