[LeetCode]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.

public class Solution {
    public int sumNumbers(TreeNode root) {
		
		if(root == null)
			return 0;
		return sumNumber(root,"0");
	}

	private int sumNumber(TreeNode root, String s) {
	
		if(root.left ==null && root.right ==null){
			return Integer.valueOf(s+root.val);
		}
		return (root.left != null ?sumNumber(root.left, s+root.val):0)+(root.right != null?sumNumber(root.right, s+root.val):0);
	}
}

参考： https://leetcode.com/discuss/47066/accepted-java-5-line-solution