class Solution {

public:

    vector<string> binaryTreePaths(TreeNode* root) {

        if(root == NULL)//二叉树为空

            return vec;

        DFS(root, to_string(root->val));

        return vec;

    }

    void DFS(TreeNode* root, string str) {

        if (root->right == NULL && root->left == NULL) {//搜索完一个叶子节点，将数据存入容器

            vec.push_back(str);

            return;

        }

        if(root->left != NULL)//防止越界取值

            DFS(root->left, str + "->" + to_string(root->left->val));//先将左子叶遍历，使用str存储递归中经过的值

        if(root->right != NULL)

            DFS(root->right, str + "->" + to_string(root->right->val));

    }

private:

    vector<string> vec;

};

/*这个应该挺容易理解*/

class Solution {

private:

 vector<string> ans;// 最终的解答

public:

 vector<string> binaryTreePaths(TreeNode* root) {

    binaryTreePaths(root, "", true);// 递归求解

    return ans;

 }

private:

 void binaryTreePaths(TreeNode* root, string s, bool isRoot) {

    if (!root) return;

    s += (isRoot ? "" : "->") + to_string(root->val);//根节点需要特殊处理

    if (!root->left && !root->right) {// 如果找到一个叶子节点

        ans.push_back(s);

        return;

    }

    binaryTreePaths(root->left, s, false);

    binaryTreePaths(root->right, s, false);

 }

};