题解 | #按之字形顺序打印二叉树#

1.BFS

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
import java.util.*;
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
    LinkedList<TreeNode> q = new LinkedList<>();
        ArrayList<ArrayList<Integer>> res = new ArrayList<>();
        boolean rev = true;
        q.add(pRoot);
        while(!q.isEmpty()){
            int size = q.size();
            ArrayList<Integer> list = new ArrayList<>();
            for(int i=0; i<size; i++){
                TreeNode node = q.poll();
                if(node == null){continue;}
                if(rev){
                    list.add(node.val);
                }else{
                    list.add(0, node.val);
                }
                q.offer(node.left);
                q.offer(node.right);
            }
            if(list.size()!=0){res.add(list);}
            rev=!rev;
        }
        return res;
    }

}