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,



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.

分析

按照二叉树的深度遍历，累计所有路径组成整数的和。

使用二叉树的递归深度优先遍历实现！

AC代码

/**

 * Definition for a binary tree node.

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

    int sumNumbers(TreeNode* root) {

        int ret = 0;

        if (!root)

            return ret;

        else if (!root->left && !root->right)

        {

            ret = root->val;

            return ret;

        }

        else

            dfs(root, root->val , ret);

        return ret;

    }

    //深度优先遍历，得到所有根节点到叶子节点的路径和

    void dfs(TreeNode *root, int val, int &sum)

    {

        if (!root->left && !root->right)

            sum += val;

        if (root->left)

        {

            dfs(root->left, val * 10 + root->left->val, sum);

        }

        if (root->right)

        {

            dfs(root->right, val * 10 + root->right->val, sum);

        }

    }

};

GitHub测试程序源码