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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.
基本思路是Recursion。我们可以这样看待问题：对于非叶子结点，我们更改它的数值（prev * 10 + currentNode.val）。然后将所有叶子结点的值相加即得到结果。
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 public class Solution { 11 public int sumNumbers(TreeNode root) { 12 return dfs(root, 0, 0); 13 } 14 15 private int dfs(TreeNode root, int prev, int sum) { 16 if (root == null) { 17 return sum; 18 } 19 prev = prev * 10 + root.val; 20 if (root.left == null && root.right == null) { 21 sum += prev; 22 return sum; 23 } 24 return dfs(root.left, prev, sum) + dfs(root.right, prev, sum); 25 } 26 }
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原文地址：http://www.cnblogs.com/ireneyanglan/p/4938378.html
