LeetCode 04 尋找兩個正序陣列的中位數
阿新 • • 發佈:2020-10-22
class BSTNode(object): def __init__(self, key, value, left=None, right=None): self.key,self.value,self.left,self.right = key,value,left,right class BST(object): def __init__(self,root=None): self.root = root @classmethod def build_from(cls,node_list): cls.size = 0 key_to_node_dict = {} for node_dict in node_list: key = node_dict['key'] key_to_node_dict[key] = BSTNode(key, value=key) for node_dict in node_list: key = node_dict['key'] node = key_to_node_dict[key] if node_dict['is_root']: root = node node.left = key_to_node_dict.get(node_dict['left']) node.right = key_to_node_dict.get(node_dict['right']) return cls(root) def _bst_search(self, subtree, key): if subtree is None: return None elif key < subtree.key: return self._bst_search(subtree.left, key) elif key > subtree.key: return self._bst_search(subtree.right, key) else: return subtree def get(self, key, default=None): node = self._bst_search(self.root, key) if node is None: return default else: return node.value def __cantains__(self,key): return self._bst_search(self.root, key) is not None def _bst_min_node(self, subtree): if subtree is None: return None elif subtree.left is None: return subtree else: return self._bst_min_node(subtree.left) def _bst_max_node(self, subtree): if subtree is None: return None elif subtree.right is None: return subtree else: return self._bst_max_node(subtree.right) def bst_min(self): node = self._bst_min_node(self.root) return node.value if node else None def bst_max(self): node = self._bst_max_node(self.root) return node.value if node else None def _bst_insert(self, subtree, key, value): if subtree is None: subtree = BSTNode(key, value) elif key < subtree.key: subtree.left = self._bst_insert(subtree.left, key, value) elif key > subtree.key: subtree.right = self._bst_insert(subtree.right, key, value) return subtree def add(self, key, value): node = self._bst_search(self.root, key) if node is not None: node.value = value return False else: self.root = self._bst_insert(self.root, key, value) self.size += 1 return True def _bst_remove(self, subtree, key): if subtree is None: return None elif key < subtree.key: subtree.left = self._bst_remove(subtree.left, key) return subtree elif key > subtree.key: subtree.right = self._bst_remove(subtree.right, key) return subtree else: #如果找到了要刪除的節點 if subtree.left is None and subtree.right is None: #是葉子 return None elif subtree.left is None or subtree.right is None: #單孩子 if subtree.left is not None: return subtree.left #返回孩子並更換父節點指向 else: return subtree.right else: #雙孩子情況,尋找邏輯後繼並且替換被刪除節點 successor_node = self._bst_min_node(subtree.right) subtree.key, subtree.value = successor_node.key, successor_node.value subtree.right = self._bst_remove(subtree.right, subtree.key) return subtree def remove(self, key): self.size -= 1 return self._bst_remove(self.root, key) NODE_LIST = [ {'key':60, 'left':12, 'right':90, 'is_root':True}, {'key':12, 'left':4, 'right':41, 'is_root':False}, {'key':4, 'left':1, 'right':None, 'is_root':False}, {'key':1, 'left':None, 'right':None, 'is_root':False}, {'key':41, 'left':29, 'right':None, 'is_root':False}, {'key':29, 'left':23, 'right':37, 'is_root':False}, {'key':23, 'left':None, 'right':None, 'is_root':False}, {'key':37, 'left':None, 'right':None, 'is_root':False}, {'key':90, 'left':71, 'right':100, 'is_root':False}, {'key':71, 'left':None, 'right':84, 'is_root':False}, {'key':100, 'left':None, 'right':None, 'is_root':False}, {'key':84, 'left':None, 'right':None, 'is_root':False}, ] def test_bst_tree(): bst = BST.build_from(NODE_LIST) for node_dict in NODE_LIST: key = node_dict['key'] assert bst.get(key) == key assert bst.get(-1) is None assert bst.bst_min() == 1 bst.add(0,0) assert bst.bst_min() == 0 bst.remove(12) assert bst.get(12) is None bst.remove(1) assert bst.get(1) is None
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