113.path-sum-ii

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


For 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(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]]
        """
        def dfs(root, s, path, res):
            if root:
                path.append(root.val)
                s -= root.val
                left = dfs(root.left, s, path, res)
                right = dfs(root.right, s, path, res)
                if not left and not right and s == 0:
                    res.append(path + [])
                path.pop()
                return True
        res = []
        dfs(root, sum, [], res)
        return res