[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.

https://oj.leetcode.com/problems/sum-root-to-leaf-numbers/

思路：递归求解，传递每个路程的和，到叶子节点累加到结果中。

public class Solution {

    private int res;

    public int sumNumbers(TreeNode root) {
        count(root, 0);
        return res;
    }

    private void count(TreeNode root, int pre) {
        if (root == null)
            return;
        int cur = pre * 10 + root.val;
        if (root.left == null && root.right == null) {
            res += cur;
            return;
        }
        count(root.left, cur);
        count(root.right, cur);

    }

    public static void main(String[] args) {
        TreeNode root = new TreeNode(5);
        root.left = new TreeNode(1);
        root.left.left = new TreeNode(2);
        root.left.right = new TreeNode(3);
        root.right = new TreeNode(2);

        System.out.println(new Solution().sumNumbers(root));
    }

}