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ZigzagLevelOrder103.java
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ZigzagLevelOrder103.java
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package Leetcode;
import java.util.*;
public class ZigzagLevelOrder103 {
/**Method1: Zigzag level order by queue; Time:O(n); Space:O(n) **/
public List<List<Integer>> zigzagLevelOrder1(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
if(root == null) {
return res;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
boolean isOrderLeft = true;
while(!queue.isEmpty()) {
Deque<Integer> list= new LinkedList<>();
int size = queue.size();
for(int i=0; i<size; i++) {
TreeNode node = queue.poll();
if(isOrderLeft) {
list.offerLast(node.val);
}else{
list.offerFirst(node.val);
}
if(node.left != null) {
queue.offer(node.left);
}
if(node.right != null) {
queue.offer(node.right);
}
}
isOrderLeft=!isOrderLeft;
res.add(new LinkedList<Integer>(list));
}
return res;
}
/**Method 2: DFS; Time:O(N); Space:O(H) **/
List<List<Integer>> res = new ArrayList();
public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
if(root == null) {
return res;
}
dfs(root, 0);
return res;
}
public void dfs(TreeNode root, int level) {
if (root == null)
return;
if(res.size() == level) {
List<Integer> newLevel = new LinkedList<>();
res.add(newLevel);
}
List<Integer> list = res.get(level);
if(level % 2 == 0){
list.add(root.val);
} else {
list.add(0, root.val);
}
dfs(root.left, level + 1);
dfs(root.right, level + 1);
}
//Definition for a binary tree node.
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode() {}
TreeNode(int val) { this.val = val; }
TreeNode(int val, TreeNode left, TreeNode right) {
this.val = val;
this.left = left;
this.right = right;
}
}
}