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

.

给定一个仅包含0-9数字的二叉树，每个根到叶的路径可以代表一个数。

一个例子 根到叶的路径 

1->2->3

 代表数123.

找出所有根到叶 数的和。

想到就是深度优先遍历。

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

public int dfs(TreeNode root, int sum) {
if (root == null)
return 0;
sum = sum * 10 + root.val;
if (root.left == null && root.right == null)
return sum;
return dfs(root.left, sum) + dfs(root.right, sum);
}
// Definition for binary tree
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) {
val = x;
}
}