129.
求路徑上的數字字串合
C# code
public class Solution {
public int SumNumbers(TreeNode root, int num = 0)
{
if (root == null) return 0;
num = num * 10 + root.val;
if (root.left == null && root.right == null) return num;
return SumNumbers(root.left, num) + SumNumbers(root.right, num);
}
}