Leetcode 113. Path Sum II

a.insert(0,root.val)
ans.append(a)

ans.append(a.insert(0,root.val))

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def pathSum(self, root, sum):
        """
        :type root: TreeNode
        :type sum: int
        :rtype: List[List[int]]
        """
        if not root:
            return []
        
        ans=[]
        if (not root.left)&(not root.right):
            if root.val==sum:
                ans.append([root.val])
            return ans
        elif not root.right:
            ans_left=self.pathSum(root.left,sum-root.val)
            if ans_left:
                for a in ans_left:
                    if a:
                        a.insert(0,root.val)
                        ans.append(a)
            return ans
        elif not root.left:
            ans_right=self.pathSum(root.right,sum-root.val)
            if ans_right:
                for a in ans_right:
                    if a:
                        a.insert(0,root.val)
                        ans.append(a)
            return ans
        else:
            ans_left=self.pathSum(root.left,sum-root.val)
            if ans_left:
                for a in ans_left:
                    if a:
                        a.insert(0,root.val)
                        ans.append(a)
            ans_right=self.pathSum(root.right,sum-root.val)
            if ans_right:
                for a in ans_right:
                    if a:
                        a.insert(0,root.val)
                        ans.append(a)
            return ans