C#•2y ago

✅ A bunch of syntax errors

I am trying to solve this puzzle https://leetcode.com/problems/n-ary-tree-preorder-traversal/ I got a couple of syntax errors at the foreach loop (like I am missing ; or , etc), but I have no idea how to apply the variable val assigned by LeetCode. Could anyone kindly point me some directions?

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(Node root.value in root.children){
            Helper(root, 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(Node root.value in root.children){
            Helper(root, ans);
        }
    }
}

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8 Replies

mtreit•2y ago

foreach(Node root.value in root.children)

foreach(Node root.value in root.children)

Well that doesn't look right for one thing root.value is not a variable. foreach should be doing something like:

foreach (Node node in root.children)
{
    var val = node.value;
    var children = node.children;
    // Do stuff
}

foreach (Node node in root.children)
{
    var val = node.value;
    var children = node.children;
    // Do stuff
}

or something like that.

morry329#OP•2y ago

Thanks a lot for your guide 🙏 I will try that again

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

One more question - my current code is like this 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(Node node in root.children){
            if (node.val == root.val){
                Helper(node, ans);
                Helper(root, 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(Node node in root.children){
            if (node.val == root.val){
                Helper(node, ans);
                Helper(root, ans);   
            }
        }
    }


}

` And I got null array [] returned instead of the pre-ordered array Could you kindly give me some hints again as to why my code returns something so null?

333fred•2y ago

You never add anything to the list

mtreit•2y ago

[] means empty not null

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

Thank you so much - I managed to get it solved Here is my code

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);
        }
    }
}

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✅ A bunch of syntax errors