leetcode 113 路径总和 ii

# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class (object):
    def pathSum(self, root, sum):
        """
        :type root: TreeNode
        :type sum: int
        :rtype: List[List[int]]
        """
        import copy
        def pathSumHelper(root, sum, ans, t=[]):
            if not root:
                return 
            t.append(root.val)
            if not root.left and not root.right and root.val == sum:
                ans.append(copy.copy(t))
            else: 
                pathSumHelper(root.left, sum-root.val, ans, t)
                pathSumHelper(root.right, sum-root.val, ans, t)
            t.pop() # 这里如果使用t.remove(root.val)在存在相同数字的情况下会出错
        
        ans = []
        pathSumHelper(root, sum, ans)
        return ans