17天【代码随想录算法训练营34期】第六章 二叉树part04（● 110.平衡二叉树 ● 257. 二叉树的所有路径 ● 404.左叶子之和 ）

110.平衡二叉树

# 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 getDepth(self, root):
        if root is None:
            return 0
        left = self.getDepth(root.left)
        right = self.getDepth(root.right)
        if left == -1 or right == -1 or abs(left - right) > 1:
            return -1
        else:
            return 1+max(left, right)
    def isBalanced(self, root: Optional[TreeNode]) -> bool:
        return self.getDepth(root) != -1

257. 二叉树的所有路径

# 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 binaryTreePaths(self, root: Optional[TreeNode]) -> List[str]:
        result = []
        temp = ""
        self.findPath(root, temp, result)
        return result


    def findPath(self, root, temp, result):
        if root is None:
            return
        elif root.left is None and root.right is None:
            if temp:
                temp += "->"
            temp += str(root.val) 
            result.append(temp)
            temp = ""

        else:
            if temp:
                temp += "->"
            temp += str(root.val)

            self.findPath(root.left, temp, result)
            self.findPath(root.right, temp, result)

404.左叶子之和

# 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 sumOfLeftLeaves(self, root: Optional[TreeNode]) -> int:
        if root is None:
            return 0
        else:
            leftVal = 0
            if root.left and (root.left.left is None) and (root.left.right is None):
                leftVal = root.left.val
            return leftVal + self.sumOfLeftLeaves(root.left) + self.sumOfLeftLeaves(root.right)