* Definition for a binary tree node.
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
vector<string> binaryTreePaths(TreeNode* root) {
void path(TreeNode* root, string s, vector<string> &res)
if(!root->left && !root->right)
res.push_back(s+to_string(root->val));
path(root->left, s+to_string(root->val)+"->", res);
path(root->right,s+to_string(root->val)+"->", res);