Regarding Tree Left view

#1

How to construct the tree from level order traversal

#2 
node *buildtree()
{
    int a;
    cin>>a;
    node *root = new node(a);
    queue<node*> q;
    q.push(root);

    while(!q.empty())
    {
        cin>>a;
        if(a!=-1)
        {
            node *temp = new node(a);
            if(q.front()->left==NULL)
            q.front()->left = temp;
            else
            {
                q.front()->right = temp;
                q.pop();
            }
            q.push(temp);
        }
        else
        {
            if(q.front()->left==NULL)
            {
                cin>>a;
                if(a==-1)
                    q.pop();
                else
                {
                    node *temp1=new node(a);
                    q.front()->right = temp1;
                    q.pop();
                    q.push(temp1);
                }
            }
            else
                q.pop();
        }
    }
    return root;
}

Just call this function

#3

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