C#•2y ago

✅ A LeetCode glitch or am I wrong with my code?

So again this is the LC puzzle https://leetcode.com/problems/binary-tree-level-order-traversal/description/ My solution is as follows;

`public class Solution {
    public IList<IList<int>> LevelOrder(TreeNode root) {
        List<IList<int>> res = new List<IList<int>>();
        if(root == null){
            return res;
        }

        Queue<TreeNode> q = new Queue<TreeNode>();
        List<int> separation = new List<int>();
        q.Enqueue(root);
        while(q.Count > 0){
            
            separation = new List<int>();
            int count = q.Count;
            for(int i = 0; i < count; i++){
                var curr = q.Dequeue();
                
                if(curr.left != null){
                    q.Enqueue(curr.left);
                }

                if(curr.right != null){
                    q.Enqueue(curr.right);
                }   
                separation.Add(curr.val);
            }
            res.Add(separation);
        }
        return res;
    }
}

`public class Solution {
    public IList<IList<int>> LevelOrder(TreeNode root) {
        List<IList<int>> res = new List<IList<int>>();
        if(root == null){
            return res;
        }

        Queue<TreeNode> q = new Queue<TreeNode>();
        List<int> separation = new List<int>();
        q.Enqueue(root);
        while(q.Count > 0){
            
            separation = new List<int>();
            int count = q.Count;
            for(int i = 0; i < count; i++){
                var curr = q.Dequeue();
                
                if(curr.left != null){
                    q.Enqueue(curr.left);
                }

                if(curr.right != null){
                    q.Enqueue(curr.right);
                }   
                separation.Add(curr.val);
            }
            res.Add(separation);
        }
        return res;
    }
}


But one line of code bothers me still. This one

int count = q.Count;` If I do like this instead of initialising the integer count:

while(q.Count > 0){
            
            separation = new List<int>();
            for(int i = 0; i < q.Count; i++){
                //DO STUFF
           }
}

while(q.Count > 0){
            
            separation = new List<int>();
            for(int i = 0; i < q.Count; i++){
                //DO STUFF
           }
}

` I get this result

Output [[3,9],[20,15],[7]] //was supposed to be [[3],[9,20],[15,7]]

Output [[3,9],[20,15],[7]] //was supposed to be [[3],[9,20],[15,7]]

` Could anyone kindly tell me it is a glitch on LC or am I wrong? (if I am wrong I appreciate it if you could point out which part of my code is wrong)

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2 Replies

Matt•2y ago

that evaluation (i < q.Count) runs every iteration so if you enqueue/dequeue stuff in q, you will end up with a different count every few iterations meanwhile, doing int count = q.Count; before the loop ensures its value doesn't change while you're iterating

morry329#OP•2y ago

Ahhhhhh I see! Thank you so much for pointing me that out 🙏 I see the error more clearly now 🔮

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✅ A LeetCode glitch or am I wrong with my code?