129. Sum Root to Leaf Numbers

 1 //New
 2 class Solution {
 3     public int sumNumbers(TreeNode root) {
 4         if(root == null) return 0;
 5         return dfs(root, 0);
 6         
 7     }
 8     
 9     public int dfs(TreeNode root, int sum) {
10         if(root == null) return 0;
11         if(root.left == null && root.right == null) {
12             return sum*10 + root.val;
13         }else {
14             return dfs(root.left, sum*10 + root.val) + dfs(root.right, sum*10 + root.val);
15         }
16         
17     }
18 }
19 
20 
21 
22 
23 
24 //Old
25 class Solution {
26     int sum = 0;
27     public int sumNumbers(TreeNode root) {
28         if(root == null) return 0;
29         dfs(root, new StringBuilder());
30         return sum;
31         
32     }
33     
34     public void dfs(TreeNode root, StringBuilder sb) {
35         if(root == null) return;
36         if(root.left == null && root.right == null) {
37             sb.append(root.val);
38             sum += Integer.parseInt(sb.toString());
39             sb.deleteCharAt(sb.length() - 1);
40         }else {
41             sb.append(root.val);
42             dfs(root.left, sb);
43             dfs(root.right, sb);
44             sb.deleteCharAt(sb.length() - 1);
45         }
46         
47     }
48 }