113.Path Sum II（append 和+的区别）

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

      5
     / 
    4   8
   /   / 
  11  13  4
 /      / 
7    2  5   1

Return:

[
[5,4,11,2],
[5,8,4,5]
]

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

class Solution:
    def pathSum(self, root, sum):
        """
        :type root: TreeNode
        :type sum: int
        :rtype: List[List[int]]
        """
        res = []
        if root is None:
            return res
        def findpath(a,root,sum):
            # a.append(root.val)
            a = a + [root.val]
            if root.left is None and root.right is None and root.val==sum:
                res.append(a)
                # print('a:',a)
                # print('res:',res)
            if root.left:
                findpath(a,root.left,sum-root.val)
            if root.right:
                findpath(a,root.right,sum-root.val)
        findpath([],root,sum)
        return res

使用append实际是修改一个列表，使用+实际是创建一个新的列表。

参考：https://www.jb51.net/article/60634.htm