[LeetCode] Binary Tree Paths

The basic idea is to start from root and add it to the current path, then we recursively visit its left and right subtrees if they exist; otherwise, we have reached a leaf node, so just add the current path to the result paths.

The code is as follows.

class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> paths;
        string path;
        treePaths(root, path, paths);
        return paths;
    }
private:
    void treePaths(TreeNode* node, string path, vector<string>& paths) {
        if (!node) return;
        path += path.empty() ? to_string(node -> val) : "->" + to_string(node -> val);
        if (!(node -> left) && !(node -> right)) {
            paths.push_back(path);
            return;
        }
        if (node -> left) treePaths(node -> left, path, paths);
        if (node -> right) treePaths(node -> right, path, paths);
    }
};