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.

Return the sum = 12 + 13 = 25

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.

Java代码

int sumhelper(TreeNode root, int levelBase) {
    if(root == null)
        return 0;

    if(root.left == null && root.right == null) {
        return levelBase + root.val; 
    }

    int nextLevelBase = (levelBase + root.val)*10 ;
    int leftSubTreeSum = sumhelper(root.left, nextLevelBase);
    int rightSubTreeSum = sumhelper(root.right, nextLevelBase);

    return leftSubTreeSum + rightSubTreeSum;
}

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