129. 求根节点到叶节点数字之和

原题

https://leetcode.cn/problems/sum-root-to-leaf-numbers/description/

思路

深度优先搜索

复杂度

时间：O(n)
空间：O(n)

Python代码

# 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:
        ans = 0 

        def dfs(root, path):
            nonlocal ans
            if not root:
                return 
            path += str(root.val)
            # 叶子节点就返回
            if root.left is None and root.right is None:
                ans += int(path)
                return 
            dfs(root.left, path)
            dfs(root.right, path)

        dfs(root, '')
        return ans 
       

Go代码

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func sumNumbers(root *TreeNode) int {
	ans := 0

	var dfs func(*TreeNode, string)
	dfs = func(root *TreeNode, path string) {
		if root == nil {
			return
		}
		path += string(root.Val + '0')
		// 遇到叶子节点就更新结果并返回
		if root.Left == nil && root.Right == nil {
			i, err := strconv.Atoi(path)
			if err != nil {
				panic(err)
			}
			ans += i
			return
		}
		dfs(root.Left, path)
		dfs(root.Right, path)
	}

	dfs(root, "")
	return ans
}