22.二叉树遍历

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。

 

广度优先遍历

 

import java.util.ArrayList;
import java.util.Stack;
import java.util.ArrayDeque;
/**
public 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> intList=new ArrayList<Integer>();
		if(root==null){
			return intList;
		}
			
              ArrayDeque<TreeNode> deque = new ArrayDeque<TreeNode>();
              deque.add(root);
              while(!deque.isEmpty()){
                    TreeNode rnode = deque.remove();
                    intList.add(rnode.val);
                    if(rnode.left!=null){
                          deque.add(rnode.left);
                    }
                    if(rnode.right!=null){
                          deque.add(rnode.right);
                    }
              }
        return intList;
    }

}