[leetcode]Sum Root to Leaf Numbers

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/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int travel(TreeNode* root , int num) {
        if(root -> left == nullptr && root -> right == nullptr) {
            return num * 10 + root -> val;
        }
        int left = 0 , right = 0;
        if(root -> left) left = travel(root -> left , num*10 + root -> val);
        if(root -> right) right = travel(root -> right , num*10 + root -> val);
        return left + right;
    }
    int sumNumbers(TreeNode *root) {
       if(root == nullptr) return 0;
       return travel(root , 0);
    }
};