[leetcode]Path Sum II @ Python

原題地址：https://oj.leetcode.com/problems/path-sum-ii/

題意：

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]
]

解題思路：這題需要將根到葉子的路徑和為sum的路徑都枚舉出來。一樣是使用遞歸。

代碼：

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

class Solution:
    # @param root, a tree node
    # @param sum, an integer
    # @return a list of lists of integers
    def pathSum(self, root, sum):
        def dfs(root, currsum, valuelist):
            if root.left==None and root.right==None:
                if currsum==sum: res.append(valuelist)
            if root.left:
                dfs(root.left, currsum+root.left.val, valuelist+[root.left.val])
            if root.right:
                dfs(root.right, currsum+root.right.val, valuelist+[root.right.val])
        
        res=[]
        if root==None: return []
        dfs(root, root.val, [root.val])
        return res