方法一：递归

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param root TreeNode类 
# @param sum int整型 
# @return bool布尔型
#
class Solution:
    def hasPathSum(self , root: TreeNode, sum: int) -> bool:
        # write code here
        if root is None:
            return False

        if not root.left and not root.right and sum-root.val == 0:
            return True
        
        return self.hasPathSum(root.left, sum - root.val) or self.hasPathSum(root.right, sum-root.val)

方法二：栈

class Solution:
    def hasPathSum(self , root: TreeNode, sum: int) -> bool:
        # write code here
        if root is None:
            return False

        s = []
        s.append((root, root.val))

        while len(s):
            tmp = s[-1]
            s.pop()
            if (not tmp[0].left) and (not tmp[0].right) and (tmp[1] == sum):
                return True
            
            if tmp[0].left:
                s.append((tmp[0].left, tmp[1] + tmp[0].left.val))
            if tmp[0].right:
                s.append((tmp[0].right, tmp[1]+ tmp[0].right.val))

        return False