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.

简单的用递归就可以实现，代码如下：

1 class Solution { 2 public: 3     int sumNumbers(TreeNode* root) { 4         dfs(root, 0); 5     } 6  7     int dfs(TreeNode * root, int curr){ 8         if(!root) 9             return 0;10         if(!root->left && !root->right)11             return curr * 10 + root->val;12         return dfs(root->left, curr    * 10 + root->val) + dfs(root->right, curr * 10 + root->val);13     }14 };

java版本的代码如下所示：

1 public class Solution { 2     public int sumNumbers(TreeNode root) { 3         return dfs(root, 0); 4     } 5  6     public int dfs(TreeNode root, int curr){ 7         if(root == null) 8             return 0; 9         if(root.left == null && root.right == null)10             return curr * 10 + root.val;11         return dfs(root.left, curr * 10 + root.val) + dfs(root.right, curr * 10 + root.val);12     }13 }