Question Definition
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.
Java Solution
public int sumNumbers(TreeNode root) {
return sumNumbersHelper(root, 0);
}
private int sumNumbersHelper(TreeNode root, int num) {
if(root == null)
return num;
int result = 0;
if(root.left != null)
result += sumNumbersHelper(root.left, num * 10 + root.val);
if(root.right != null)
result += sumNumbersHelper(root.right, num * 10 + root.val);
if(root.left == null && root.right == null)
result = num * 10 + root.val;
return result;
}
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