129. 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.

 

public int SumNumbers(TreeNode root) {
        return SumSub(root,0);
    }
    
    
    public int SumSub(TreeNode root, int num)
    {
         if(root == null) return num;
         int nextNum = num*10 + root.val;
         if(root.left == null && root.right == null) return num*10 + root.val;
         if(root.left == null) return SumSub(root.right,nextNum);
         if(root.right == null) return SumSub(root.left,nextNum);
         return SumSub(root.left,nextNum) + SumSub(root.right,nextNum);
    }