Sum Root to Leaf Numbers

1.题目

原题链接: http://oj.leetcode.com/problems/sum-root-to-leaf-numbers/

2.算法

用先序遍历的递归方式做

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