129. Sum Root to Leaf Numbers

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.

For example,

    1   / \  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

求根到子树的路径的所有和。

常用回溯法。

每当dfs访问到子树时，把和加上即可。

 int sum=0;public int sumNumbers(TreeNode root){if(root==null)return 0;inorder(root, String.valueOf(root.val));return sum;}private void inorder(TreeNode t,String s){if(t.left!=null)inorder(t.left, s+t.left.val);if(t.left==null&&t.right==null)sum+=Integer.parseInt(s);if(t.right!=null)inorder(t.right, s+t.right.val);}