Binary Tree Paths

LeetCode 257

DFS

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

class Solution:
    def binaryTreePaths(self, root):
        """
        :type root: TreeNode
        :rtype: List[str]
        """       
        self.res = []
        def dfs(root, path):
            if not root.left and not root.right:
                self.res.append(path+str(root.val))           
            if root.left:
            # 第二次複習少加了"path" (path+str(root.val)+"->")
            # 出來會少個root很神奇
                dfs(root.left, path+str(root.val)+"->")
            if root.right:
                dfs(root.right, path+str(root.val)+"->")      
        dfs(root,"")
        return self.res

Stack

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

class Solution:
    def binaryTreePaths(self, root):
        """
        :type root: TreeNode
        :rtype: List[str]
        """
        if not root:
            return []
        stack = [(root, "")]
        res = []
        while stack:
            node, strr = stack.pop()
            
            if node:
                if not node.left and not node.right:
                    res.append(strr+str(node.val))                
                if node.left:
                    stack.append((node.left, strr + str(node.val) + "->"))
                if node.right:
                    stack.append((node.right, strr + str(node.val) + "->"))
        return res