问题描述：

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 number123.

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.

代码：

   public int sumNumbers(TreeNode root) {  //Java
        if (root == null)
            return 0;
        return sumR(root, 0);
    }
    public int sumR(TreeNode root, int x) {
        if (root.right == null && root.left == null)
            return 10 * x + root.val;
        int val = 0;
        if (root.left != null)
            val += sumR(root.left, 10 * x + root.val);
        if (root.right != null)
            val += sumR(root.right, 10 * x + root.val);
        return val;
    }

[leetcode]Sum Root to Leaf Numbers