Given the root of a binary tree, return the postorder traversal of its nodes’ values.
Example 1:
Input: root = [1,null,2,3] Output: [3,2,1]
Example 2:
Input: root = [] Output: []
Example 3:
Input: root = [1] Output: [1]
Constraints:
[0, 100].-100 <= Node.val <= 100
class Solution {
public List<Integer> postorderTraversal(TreeNode root) {
List<Integer> list = new ArrayList<>();
helper(root,list);
return list ;
}
public void helper(TreeNode root , List<Integer> list ){
if(root==null){
return ;
}
helper(root.left , list );
helper(root.right, list);
list.add(root.val);
}
}
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