题目
请实现一个函数按照之字形顺序打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右到左的顺序打印，第三行再按照从左到右的顺序打印，其他行以此类推。
实现
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public class {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public (int val) {
this.val = val;
}
}
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public ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
ArrayList<ArrayList<Integer>> results = new ArrayList<>();
if (pRoot != null) {
Stack<TreeNode>[] stack = (Stack<TreeNode>[]) new Stack[2];
for (int i = 0; i < 2; i++)
stack[i] = new Stack<>();
int idx = 0;
stack[idx].push(pRoot);
while (!stack[idx].isEmpty()) {
ArrayList<Integer> result = new ArrayList<>();
int start = 0;
int end = stack[idx].size();
while (start++ < end){
TreeNode node = stack[idx].pop();
result.add(node.val);
if (idx == 0) {
if (node.left != null)
stack[1-idx].push(node.left);
if (node.right != null)
stack[1-idx].push(node.right);
}
else {
if (node.right != null)
stack[1-idx].push(node.right);
if (node.left != null)
stack[1-idx].push(node.left);
}
}
idx = 1 - idx;
results.add(result);
}
}
return results;
}
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