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算法训练第十五天

news 2025/9/20 6:56:31

110.平衡二叉树

代码：

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:def isBalanced(self, root: Optional[TreeNode]) -> bool:ans = [True]a = self.find(root,ans)return ans[0]def find(self,node,ans):if node is None:return 0left = self.find(node.left,ans)right = self.find(node.right,ans)if abs(left-right)>1:ans[0] = Falsereturn max(left,right)+1

257.二叉树的所有路径

代码：

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):import copydef binaryTreePaths(self, root):""":type root: Optional[TreeNode]:rtype: List[str]"""ans = []res = []self.find(root,res,ans)return ansdef find(self,node,res,ans):res.append(str(node.val))if node.left is None and node.right is None:ans.append(copy.deepcopy('->'.join(res)))res.pop()returnif node.left:self.find(node.left,res,ans)if node.right:self.find(node.right,res,ans)res.pop()

404.左叶子之和

代码：

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):def sumOfLeftLeaves(self, root):""":type root: Optional[TreeNode]:rtype: int"""ans = []lf=Falseself.find(root,ans,lf)return sum(ans)def find(self,node,ans,lf):if node.left is None and node.right is None:if lf:ans.append(node.val)if node.left:self.find(node.left,ans,True)if node.right:self.find(node.right,ans,False)

222.完全二叉树的节点个数

代码：

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):def countNodes(self, root):""":type root: Optional[TreeNode]:rtype: int"""ans = []self.find(root,ans)return len(ans)def find(self,node,ans):if node:ans.append(node.val)self.find(node.left,ans)self.find(node.right,ans)