leetcode129. 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

  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.

算法：基于二叉树前序遍历算法，累加所有路径代表的数字。

1
2
3
4
5
6
7
8
9

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