LeetCode: Sum Root to Leaf Numbers

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LeetCode: 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.

地址：https://oj.leetcode.com/problems/sum-root-to-leaf-numbers/

演算法：用遞迴的方法完成的。首先分別計算左右子樹的和，並且把子樹中所有葉子節點的深度記錄下來，然後根的和=左子樹的和+右子樹的和+根的值*pow10（葉子節點的深度）。代碼：

 1 /** 2  * Definition for binary tree 3  * struct TreeNode { 4  *     int val; 5  *     TreeNode *left; 6  *     TreeNode *right; 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8  * }; 9  */10 class Solution {11 public:12     int sumNumbers(TreeNode *root) {13         vector<int> level;14         if(!root)   return 0;15         return sum(root,level);16     }17     int sum(TreeNode *root, vector<int> &level){18         if(!root)   return -1;19         if(!root->left && !root->right){20             level.push_back(1);21             return root->val;22         }23         vector<int> left;24         int left_sum = sum(root->left,left);25         vector<int> right;26         int right_sum = sum(root->right,right);27         int total_sum = 0;28         if(left_sum >= 0){29             total_sum += left_sum;30             vector<int>::iterator it = left.begin();31             for(; it != left.end(); ++it){32                 total_sum += (root->val * int(pow10(*it)));33                 level.push_back(*it + 1);34             }35         }36         if(right_sum >= 0){37             total_sum += right_sum;38             vector<int>::iterator it = right.begin();39             for(; it != right.end(); ++it){40                 total_sum += (root->val * int(pow10(*it)));41                 level.push_back(*it + 1);42             }43         }44         return total_sum;45     }46 };

 

LeetCode: Sum Root to Leaf Numbers