LeetCode 129 Sum Root to Leaf Numbers (DFS)

Given a binary tree containing digits from  0-9  only, each root-to-leaf path could represent a number.
An example is the root-to-leaf path  1->2->3  which represents the number  123 .
Find the total sum of all root-to-leaf numbers.
Note: A leaf is a node with no children.
Example:

Input: [1,2,3]
    1
   / \
  2   3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.

Example 2:

Input: [4,9,0,5,1]
    4
   / \
  9   0
 / \
5   1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.

タイトルリンク:https://leetcode.com/problems/sum-root-to-leaf-numbers/
テーマ分析:水DFS
0 ms、タイム100%

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    
    public int ans = 0;
    
    public int sumNumbers(TreeNode root) {
        if (root == null) {
            return 0;
        }
        dfs(root, 0);
        return ans;
    }
    
    public void dfs(TreeNode root, int val) {
        if (root.left == null && root.right == null) {
            ans += val * 10 + root.val;
            return;
        }
        if (root.left != null) {
            dfs(root.left, val * 10 + root.val);
        }
        if (root.right != null) {
            dfs(root.right, val * 10 + root.val);
        }
    }
}