剑指Offer_60

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题目

从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。

解题思路

二叉树层序遍历

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import java.util.ArrayList;
import java.util.LinkedList;
/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;
    public TreeNode(int val) {
        this.val = val;
    }
}
*/
public class Solution {
    ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
    	ArrayList<ArrayList<Integer>> AA = new ArrayList<>();
        if(pRoot == null){
            return AA;
        }
        LinkedList<TreeNode> nodeList = new LinkedList<>();
        nodeList.add(pRoot);
        while(!nodeList.isEmpty()){
            ArrayList<Integer> A = new ArrayList<>();
            
            int size = nodeList.size();
            for(int i = 0; i < size; ++i){
            	TreeNode node = nodeList.removeFirst();
                A.add(node.val);
                if(node.left != null){
                    nodeList.addLast(node.left);
                }
                if(node.right != null){
                    nodeList.addLast(node.right);
                }
            }
            AA.add(A);
        }
        return AA;
    }
    
}