129. Sum Root to Leaf Numbers

129. Sum Root to Leaf Numbers

 

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def sumNumbers(self, root: Optional[TreeNode]) -> int:
        stack = []
        def dfs(node, curString):
            if not node:
                return 
            
            curString += str(node.val)

            if not node.left and not node.right: # 리프 노드면
                stack.append(int(curString))
            
            dfs(node.left, curString)
            dfs(node.right, curString)

        dfs(root, "")

        return sum(stack)

 

 

https://youtu.be/Jk16lZGFWxE?si=Bda3XXK1h8wfwLh-

 

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def sumNumbers(self, root: Optional[TreeNode]) -> int:
        def dfs(cur, num):
            if not cur:
                return 0

            num = num*10 + cur.val
            if not cur.left and not cur.right: # 리프 노드면 
                return num
                            
            return dfs(cur.left, num) + dfs(cur.right, num)

        return dfs(root, 0)

        """
         1
        2 3

        루드: 0 * 10 + 1 = 1
        왼쪽: 1 * 10 + 2 = 12
        오른쪽: 1 * 10 + 3 = 13
        """