64 lines
1.8 KiB
Java
64 lines
1.8 KiB
Java
/*
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* @lc app=leetcode id=103 lang=java
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*
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* [103] Binary Tree Zigzag Level Order Traversal
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* public class TreeNode {
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* int val;
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* TreeNode left;
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* TreeNode right;
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* TreeNode() {}
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* TreeNode(int val) { this.val = val; }
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* TreeNode(int val, TreeNode left, TreeNode right) {
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* this.val = val;
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* this.left = left;
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* this.right = right;
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* }
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* }
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*/
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class Solution {
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public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
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if(root == null) {
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return new ArrayList<>();
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}
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LinkedList<TreeNode> queue = new LinkedList<>();
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ArrayList<TreeNode> stack = new ArrayList<>();
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queue.add(root);
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List<List<Integer>> ret = new ArrayList<>();
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List<Integer> curLayer = new ArrayList<>();
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TreeNode lastLayerNode = null, curLayerNode;
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while(!queue.isEmpty()) {
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TreeNode tmp = queue.pollFirst();
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curLayer.add(tmp.val);
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if(tmp.left != null) {
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// queue.add(tmp.left);
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stack.addLast(tmp.left);
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}
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if(tmp.right != null) {
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// queue.add(tmp.right);
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stack.addLast(tmp.right);
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}
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if(tmp == lastLayerNode || lastLayerNode == null) {
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// while()
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// ret.add(curLayer);
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// curLayer = new ArrayList<>();
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// lastLayerNode = curLayerNode;
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while(!stack.isEmpty()) {
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curLayerNode = stack.pollLast();
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queue.add(curLayerNode);
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}
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lastLayerNode = curLayerNode;
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ret.add(curLayer);
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curLayer = new ArrayList<>();
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}
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}
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return ret;
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}
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}
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// @lc code=end
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