Sum Root to Leaf Numbers
Given a binary tree containing digits from0-9
only, each root-to-leaf path could represent a number.
An example is the root-to-leaf path1->2->3
which represents the number123
.
Find the total sum of all root-to-leaf numbers.
Note: A leaf is a node with no children.
Example
Example 1:
Input: [1,2,3]
1
/ \
2 3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.
Example 2:
Input: [4,9,0,5,1]
4
/ \
9 0
/ \
5 1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.
Note
Divide and conquer
num是递归传递的参数
num = num * 10 + root.val
一直到叶子结点
Code
class Solution {
public int sumNumbers(TreeNode root) {
return helper(root, 0);
}
private int helper(TreeNode root, int num) {
if (root == null) {
return 0;
}
num = num * 10 + root.val;
if (root.left == null && root.right == null) {
return num;
}
return helper(root.left, num) + helper(root.right, num);
}
}
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