LeetCode----sum-root-to-leaf-numbers

题目描述

Given a binary tree containing digits from0-9only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path1->2->3which represents the number123.

Find the total sum of all root-to-leaf numbers.

For example,

    1   / \  2   3

The root-to-leaf path1->2represents the number12.
The root-to-leaf path1->3represents the number13.

Return the sum = 12 + 13 =25.

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思路：递归调用先序遍历。

C/C++ (clang++ 3.3)

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/**

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 * Definition for binary tree

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 * struct TreeNode {

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 *     int val;

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 *     TreeNode *left;

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 *     TreeNode *right;

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

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 * };

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 */

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class Solution {

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public:

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    int sumNumbers(TreeNode *root) {

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        int sum = 0;

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        return preorderNumbers(root, sum);

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    }

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    int preorderNumbers(TreeNode *root, int sum){

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        if (!root)

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            return 0;

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        sum = 10*sum + root->val;

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

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            return sum;//递归出口

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        return preorderNumbers(root->left, sum)+preorderNumbers(root->right, sum);

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    }

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};

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