誤差總和二叉搜索樹

Question

我如何總結這裏面BST（二叉搜索樹） 我嘗試這個代碼，但給的值Me錯誤

def total(bst): 
    total = 0 
    bst = BST() 
    node = bst._root 
    if node == None: 
     total = 0 
    if node._right is not None and node._left is not None: 
     total = total + node._right + node._left 
    elif node._right is not None and node._left is None: 
     total = total + node._right 
    else: 
     total = total + node._left 
    return total 

，我得到它的誤差值：

if node._right is not None and node._left is not None: 
AttributeError: 'NoneType' object has no attribute '_right' 

而且，我想這種方式給了我零

bst.comparision = 0 
x= bst.comparision 
return x 

Answer 1

也許你想要一個elif？

def total(bst): 
    total = 0 
    bst = BST() 
    node = bst._root 
    if node == None: 
     total = 0 
    # elif, not if? 
    elif node._right is not None and node._left is not None: 
     total = total + node._right + node._left 
    elif node._right is not None and node._left is None: 
     total = total + node._right 
    else: 
     total = total + node._left 
    return total 

當你的代碼編寫，如果node == None，然後設置total = 0並立即去檢查node._right（不因爲None存在不具有_right屬性）

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此外，順便說一下，if node is None通常優於if node == None，因爲None是單身人士。