LeetCode题解：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.

题意：给定二叉树，其从根结点到叶子结点的路径代表一个整数，求所有路径的和

解决思路：dfs

代码：

public class Solution {
    public int sumNumbers(TreeNode root) {
        if(root == null){
            return 0;
        }

        return dfs(root, 0);
    }

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

        int result = 0;

        if(root.left != null){
            result += dfs(root.left, sum * 10 + root.val);
        }

        if(root.right != null){
            result += dfs(root.right, sum * 10 + root.val);
        }

        return result;
    }
}