Given a binary tree containing digits from0-9only, each root-to-leaf path could represent a number.
An example is the root-to-leaf path1->2->3which represents the number123.
Find the total sum of all root-to-leaf numbers.
For example,
1 / \ 2 3
The root-to-leaf path1->2represents the number12.The root-to-leaf path1->3represents the number13.
Return the sum = 12 + 13 =25.
分析： 从root到leaf一条路径上的和之前是做过的，这里稍微变化一下， 上一层的value * 10 再加当前层 value 就是所要维护的值， 利用Java pass by value的特性，， 用一个List<Integer> res来保存两个变量， res.get(0)回溯跟踪得到某一条root到leaf的数字是多少， root.get(1)维护遍历过的各个路径得到的数字和。
/** * Definition for a binary tree node. * public class TreeNode { *int val; *TreeNode left; *TreeNode right; *TreeNode(int x) { val = x; } * } */public class Solution {public int sumNumbers(TreeNode root) {if(root == null){return 0;}List<Integer> res = new ArrayList<>();res.add(0);res.add(0);helper(res, root);return res.get(1);}private void helper(List<Integer> res, TreeNode root){if(root == null){return;}if(root.left == null && root.right == null){res.set(1, res.get(1) + res.get(0) * 10 + root.val);return;}res.set(0, res.get(0) * 10 + root.val);helper(res, root.left);helper(res, root.right);res.set(0, (res.get(0) – root.val) / 10);}}
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醒来第一眼看见的是他，然后倒头继续睡。这就是我想要的幸福。
