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M103_ZIGZAG_Traversal.java
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M103_ZIGZAG_Traversal.java
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/**
* 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;
* }
* }
*/
class Solution {
public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
Queue<TreeNode> q = new LinkedList<TreeNode>();
List<List<Integer>> result = new ArrayList<List<Integer>>();
List<TreeNode> rev_q = new ArrayList<TreeNode>();
boolean flag = true;
if(root==null)
return result;
q.offer(root);
while(!q.isEmpty()){
int level = q.size();
List<Integer> li = new ArrayList<Integer>();
for(int i=0; i<level; ++i){
TreeNode node = q.poll();
if (flag==true)
li.add(node.val);
else
li.add(0,node.val); // adds elements in the first position which traverses the tree in reverse direction
if(node.left!=null)
q.add(node.left);
if(node.right!=null)
q.add(node.right);
}
// Better way is to do: flag= !flag
if(flag==true)
flag=false;
else
flag=true;
result.add(li);
}
return result;
}
}