LeetCode OJ：Sum Root to Leaf Numbers（根到叶节点数字之和）

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.

简单的用递归就可以实现，代码如下：

class Solution {
public:
    int sumNumbers(TreeNode* root) {
        dfs(root, 0);
    }

    int dfs(TreeNode * root, int curr){
        if(!root)
            return 0;
        if(!root->left && !root->right)
            return curr * 10 + root->val;
        return dfs(root->left, curr    * 10 + root->val) + dfs(root->right, curr * 10 + root->val);
    }
};

java版本的代码如下所示：

public class Solution {
    public int sumNumbers(TreeNode root) {
        return dfs(root, 0);
    }

    public int dfs(TreeNode root, int curr){
        if(root == null)
            return 0;
        if(root.left == null && root.right == null)
            return curr * 10 + root.val;
        return dfs(root.left, curr * 10 + root.val) + dfs(root.right, curr * 10 + root.val);
    }
}