C#•2y ago

❔ ✅ Missing a first element of the output

So I am on this LeetCode puzzle https://leetcode.com/problems/n-ary-tree-preorder-traversal/?envType=study-plan&id=level-1 My code is here right now

public class Solution {
    public IList<int> Preorder(Node root) {
        List<int> ans = new List<int>();
        if(root == null){
            return ans;
        }
        Helper(root, ans);
        return ans;
        
    }

    public void Helper(Node root, List<int> ans){
        foreach(var node in root.children){
            
            ans.Add(node.val);
            Helper(node, ans);
        }
    }
}

public class Solution {
    public IList<int> Preorder(Node root) {
        List<int> ans = new List<int>();
        if(root == null){
            return ans;
        }
        Helper(root, ans);
        return ans;
        
    }

    public void Helper(Node root, List<int> ans){
        foreach(var node in root.children){
            
            ans.Add(node.val);
            Helper(node, ans);
        }
    }
}

It is still missing a first element in the List array as per screenshot. Could anyone kindly tell me why?

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7 Replies

rotor_•2y ago

@morry329 you seem to have forgotten the root node

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

morry329#OP•2y ago

Thanks a lot - just one more question. So I have added the root node in the PreOrder method, it worked:

public class Solution {
    public IList<int> Preorder(Node root) {
        List<int> ans = new List<int>();
        if(root == null){
            return ans;
        }
        ans.Add(root.val);
        Helper(root, ans);
        return ans;
        
    }

    public void Helper(Node root, List<int> ans){
        foreach(var node in root.children){
            
         
            ans.Add(node.val);
            
            Helper(node,ans);
        }
    }
}

public class Solution {
    public IList<int> Preorder(Node root) {
        List<int> ans = new List<int>();
        if(root == null){
            return ans;
        }
        ans.Add(root.val);
        Helper(root, ans);
        return ans;
        
    }

    public void Helper(Node root, List<int> ans){
        foreach(var node in root.children){
            
         
            ans.Add(node.val);
            
            Helper(node,ans);
        }
    }
}

rotor_•2y ago

...What's the question?

morry329#OP•2y ago

Sorry I forgot to delete the question part, I just resolved it myself 🙂

rotor_•2y ago

Ah nice congrats udidit

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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Programming

❔ ✅ Missing a first element of the output