LetCode 129. 求根到叶子节点数字之和

// 深度优先遍历，到达叶子节点时，将目前的数字加到结果里
class Solution {
public:
    int sumNumbers(TreeNode* root) {
        int res = 0;
        vector<int> tmp;
        sumNumbers(root, res, tmp);
        return res;
    }
    
    void sumNumbers(TreeNode* root, int& res, vector<int>& tmp){
        if (root == NULL)
            return;
        tmp.push_back(root->val);
        if (root->left == NULL && root->right == NULL){
            res += add(tmp);
            tmp.pop_back();
            return;
        }
        if (root->left == NULL)
            sumNumbers(root->right, res, tmp);
        else if (root->right == NULL)
            sumNumbers(root->left, res, tmp);
        else
            sumNumbers(root->left, res, tmp), sumNumbers(root->right, res, tmp);
        //push后记得pop
        tmp.pop_back();
    }
    
    int add(vector<int>& tmp){
        int cnt = 0;
        for(int i = 0; i < tmp.size(); ++i)
            cnt = 10 * cnt + tmp[i];
        return cnt;
    }
};

static int x=[](){
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();