Sum Root to Leaf Numbers

鏈接：https://oj.leetcode.com/problems/sum-root-to-leaf-numbers/

描述：

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.

方法：

遍歷就行了，dfs。

代碼如下：

    int sumNumbers(TreeNode *root) {
    	if(root == NULL) return 0;
    	int sum = 0;
    	dfs(root, 0, sum);
    	return sum;
    }
    
    void dfs(TreeNode *root, int num, int &sum)
    {
    	num = num*10 + root->val;
    	if(root->left == NULL && root->right == NULL)
    	{
    		sum += num;
    		return;
    	}
    	if( root->left )
    		dfs(root->left, num, sum);
    	if(root->right)
    		dfs(root->right, num, sum);
    }