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
  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.

思路

我们利用深度优先遍历，可以分别得到所有可能出现的数字。然后将这些数字分别求和即可。

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int sum = 0;
    public void appendnumber(TreeNode cur, int number){
        int cur_val = cur.val;
        if(cur.left != null) appendnumber(cur.left, number*10 + cur_val);
        if(cur.right != null) appendnumber(cur.right, number*10 + cur_val);
        if (cur.left == null && cur.right == null) sum += number * 10 + cur_val;
    }
    public int sumNumbers(TreeNode root) {
        if (root != null) appendnumber(root, 0);
        return sum;
    }
}