129.SumRoot 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.
方法
实际上这道题很简单，刷LeetCode这么长时间了，这道题都不会做有点不应该，要好好反思！！！使用正常解决二叉树的方法–先序遍历，判断条件为节点为空，或者节点的左右子树都为空。
/**
* 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) {
return sum(root, 0);
}
public int sum(TreeNode root, int sum){
if(root == null){
return 0;
}
if(root.left == null && root.right == null){
return sum*10 + root.val;
}
return sum(root.left,sum*10 + root.val) + sum(root.right,sum*10 + root.val);
}
}