题目描述
请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推。
import java.util.ArrayList;
import java.util.Stack;
public class Solution {
public ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
if(pRoot == null)
return new ArrayList<ArrayList<Integer>>();
Stack<TreeNode> stack1 = new Stack<TreeNode>();
Stack<TreeNode> stack2 = new Stack<TreeNode>();
ArrayList<ArrayList<Integer>> array = new ArrayList<ArrayList<Integer>>();
ArrayList<Integer> a = new ArrayList<Integer>();
stack1.push(pRoot);
while(!stack1.isEmpty() || !stack2.isEmpty()) {
while(!stack1.isEmpty()) {
TreeNode node = stack1.pop();
a.add(node.val);
if(node.left != null)
stack2.push(node.left);
if(node.right != null)
stack2.push(node.right);
}
if(a.size() > 0)
array.add(a);
a = new ArrayList<Integer>();
while(!stack2.isEmpty()) {
TreeNode node = stack2.pop();
a.add(node.val);
if(node.right != null) {
stack1.push(node.right);
}
if(node.left != null) {
stack1.push(node.left);
}
}
if(a.size() > 0)
array.add(a);
a = new ArrayList<Integer>();
}
return array;
}
}
