Description
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,
tree
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.
Solution
DFS
注意递归的终止条件是leaf node，而非null。
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int sumNumbers(TreeNode root) {
return sumNumbersRecur(root, 0);
}
public int sumNumbersRecur(TreeNode root, int sum) {
if (root == null) {
return 0;
}
if (root.left == null && root.right == null) {
return sum * 10 + root.val;
}
return sumNumbersRecur(root.left, sum * 10 + root.val)
+ sumNumbersRecur(root.right, sum * 10 + root.val);
}
}
