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);
 }
};