[leetcode]Sum Root to Leaf Numbers

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;    }