[leetcode_129] Sum Root to Leaf Numbers

A binary tree where each node from root to leaf stores a digit from 0 to 9. Calculate the sum of all numbers formed from root to leaf paths. Search from the root to each leaf node, convert the string to a number, and add it to the result.

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class Solution {
public:
    int ConvertNumber(string &tmpNumber) {
        int number = 0;
        for(int i = 0;i < tmpNumber.length();i++) {
            number += (tmpNumber[tmpNumber.length() - 1 - i] - '0')*pow(10.0,i);
        }
        return number;
    }
    void AddNextLevel(TreeNode *node,int &sum,string tmpNumber) {
        tmpNumber.push_back(node->val + '0' - 0);
        if(node->left == NULL && node->right == NULL) {
            sum += ConvertNumber(tmpNumber);
            return ;
        }
        if(node->left != NULL) {
            AddNextLevel(node->left,sum,tmpNumber);
        }
        if(node->right != NULL) {
            AddNextLevel(node->right,sum,tmpNumber);
        }
    }
    int sumNumbers(TreeNode *root) {
        int sum = 0;
        if(root == NULL)return sum;
        string tmpNumber = "";
        AddNextLevel(root,sum,tmpNumber);
        return sum;
    }
};