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PrintFromTopToBottomBinaryTree.java

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/**

* 剑指Offer，从上到下打印二叉树

*/

import java.util.ArrayList;

import java.util.LinkedList;

import java.util.Queue;

import javax.swing.tree.TreeNode;

/**

public class TreeNode {

int val = 0;

TreeNode left = null;

TreeNode right = null;

public TreeNode(int val) {

this.val = val;

}

}

*/

public class PrintFromTopToBottomBinaryTree {

public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {

ArrayList<Integer> result = new ArrayList<>();

if (root == null) {

return result;

}

Queue<TreeNode> q = new LinkedList<>();

q.offer(root);

while (!q.isEmpty()) {

TreeNode node = q.poll();

result.add(node.val);

if (node.left != null) {

q.offer(node.left);

}

if (node.right != null) {

q.offer(node.right);

}

}

return result;

}

}