leetcode: Sum Root to Leaf Numbers

martin_liang

于 2014-03-18 15:33:46 发布

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分类专栏： C++/C 算法 leetcode

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本文介绍了一种算法，用于计算二叉树中所有从根节点到叶子节点的路径所代表数字的总和。通过递归遍历的方式，将每个路径上的数字累加并返回最终的总和。

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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 number123.

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.

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    void sumNumbersInt(TreeNode *root, int lastSum, int &totalSum)
    {
        if (!root)
            return;
        
        int curSum = lastSum*10 + root->val;
        if (root->left == NULL && root->right == NULL)
        {
            totalSum += curSum;
            return;
        }

        sumNumbersInt(root->left, curSum, totalSum);
        sumNumbersInt(root->right, curSum, totalSum);
    }
    
public:
    int sumNumbers(TreeNode *root) {
        
        if (!root)
            return 0;
            
        int totalSum = 0;
        
        sumNumbersInt(root, 0, totalSum);
        
        return totalSum;
    }
};