LeetCode -- Sum Root to Leaf Numbers
題目描述：
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.
思路：
DFS問題，即從根節點出發進入統計（存為string s），如果左節點不為空，進入左子樹統計；如果右子樹不為空進入右子樹統計。如果是葉子節點，記錄狀態放入總結果（List
result）。
遍歷完之後，再遍歷一遍result轉為整形累加計算結果即可。
實現代碼：
/**
* Definition for a binary tree node.
* public class TreeNode {
* public int val;
* public TreeNode left;
* public TreeNode right;
* public TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int SumNumbers(TreeNode root)
{
if(root == null){
return 0;
}
var ret = new List();
Sum(root, ,ref ret);
var s = 0;
for(var i = 0;i < ret.Count; i++){
s += int.Parse(ret[i]);
}
return s;
}
private void Sum(TreeNode root, string s,ref List result)
{
if(root.left == null && root.right == null){
result.Add(s + root.val);
return;
}
if(root.left != null){
Sum(root.left, s + root.val, ref result);
}
if(root.right != null){
Sum(root.right, s + root.val, ref result);
}
}
}
