LeetCode 257. Binary Tree Paths

Given a binary tree, return all root-to-leaf paths.

For example, given the following binary tree:

1
/   \
2     3
\
5

All root-to-leaf paths are:

["1->2->5", "1->3"]

/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<string> v;
void path(TreeNode* root, string s){
if(!root->left && !root->right){
ostringstream o;
o << root->val;
if(s != "") s = s + "->" + o.str();
else s = o.str();
v.push_back(s);
}
if(root->left){
ostringstream o;
o << root->val;
string tmp = s;
if(tmp != "") tmp = tmp + "->" + o.str();
else tmp = o.str();
path(root->left, tmp);
}
if(root->right){
ostringstream o;
o << root->val;
string tmp = s;
if(tmp != "") tmp = tmp + "->" + o.str();
else tmp = o.str();
path(root->right, tmp);
}
}
vector<string> binaryTreePaths(TreeNode* root) {
if(root == NULL) return v;
path(root, "");
return v;
}
};