*Sum root to leaf number

题目：

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) {
    if(root == null) 
        return 0;
 
    return dfs(root, 0, 0);
}
 
public int dfs(TreeNode node, int num, int sum){
    if(node == null) return sum;
 
    num = num*10 + node.val;
 
    // leaf
    if(node.left == null && node.right == null) {
        sum += num;
        return sum;
    }
 
    // left subtree + right subtree
    sum = dfs(node.left, num, sum) + dfs(node.right, num, sum);
    return sum;
}

 reference: http://www.programcreek.com/2014/05/leetcode-sum-root-to-leaf-numbers-java/

*Sum root to leaf number

原文：http://www.cnblogs.com/hygeia/p/4766087.html