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Day-22 Binary Tree Zigzag Level Order Traversal
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Day-22 Binary Tree Zigzag Level Order Traversal
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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) {
List<List<Integer>> res=new ArrayList<>();
if(root==null) return res;
boolean reverse=false;
Queue<TreeNode> st=new LinkedList<>();
st.add(root);
while(!st.isEmpty()){
int size=st.size();
List<Integer> l=new ArrayList<>();
while(size-->0){
TreeNode temp=st.remove();
l.add(temp.val);
if(temp.left!=null){
st.add(temp.left);
}
if(temp.right!=null){
st.add(temp.right);
}
}
if(reverse){
Collections.reverse(l);
}
reverse=!reverse;
res.add(l);
}
return res;
}
}
class Solution {
public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
List<List<Integer>> res=new ArrayList<>();
if(root==null) return res;
helper(root,0,res);
return res;
}
void helper(TreeNode node,int level,List<List<Integer>> res){
if(node==null){
return;
}
if(res.size()==level){
res.add(new ArrayList<>());
}
if(level%2==0){
res.get(level).add(node.val);
}else{
res.get(level).add(0,node.val);
}
helper(node.left,level+1,res);
helper(node.right,level+1,res);
}
}