Leetcode-144 Binary Tree Preorder Traversal Solution in Java | Hindi Coding Community

 

Given the root of a binary tree,you have to return the preorder traversal of its nodes' values. Find the preorder of this binary tree.

 

Example 1:

Input: root = [1,null,2,3]
Output: [1,2,3]

Example 2:

Input: root = []
Output: []

Example 3:

Input: root = [1]
Output: [1]

 

Constraints:

• The number of nodes in the tree is in the range [0, 100].
• -100 <= Node.val <= 100

Java Code :

class Solution {

public List<Integer> preorderTraversal(TreeNode root) {

List<Integer> al=new ArrayList<Integer>();

Stack<TreeNode> st=new Stack<TreeNode>();

TreeNode curr=root;

st.push(root);

while(!st.isEmpty())

{

while(curr!=null)

{

al.add(curr.val);

if(curr.right!=null)

{

st.push(curr.right);

}

curr=curr.left;

}

curr=st.pop();

}

return al;

}

}