Java for LeetCode 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.

解题思路：

递归，JAVA实现如下：

    static public int sumNumbers(TreeNode root) {
    	if(root==null)
    		return 0;
        return sumNumbers(root,0);
    }
    public static int sumNumbers(TreeNode root,int res) {
    	if(root.left==null&&root.right==null)
    		return res*10+root.val;
    	if(root.left==null)
    		return sumNumbers(root.right,res*10+root.val);
    	if(root.right==null)
    		return sumNumbers(root.left,res*10+root.val);
    	return sumNumbers(root.left,res*10+root.val)+sumNumbers(root.right,res*10+root.val);
    }