129. Sum Root to Leaf Numbers

class Solution {public:    int ans;    int sumNumbers(TreeNode* root) {        ans = 0;        if(!root) return 0;        pre(root, 0);        return ans;    }    void pre(TreeNode *p, int preSum){        if(!p) return;        if(!p->left && !p->right){            cout<<(preSum * 10 + p->val)<<endl;            ans += (preSum * 10 + p->val);        }        if(p->left) pre(p->left, preSum * 10 + p->val);        if(p->right) pre(p->right, preSum * 10 + p->val);    }};