257. Binary Tree Paths

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

For example, given the following binary tree:

Solution1:

class Solution {

    public List<String> binaryTreePaths(TreeNode root) {

        List<String> ans = new ArrayList<>();

        if (root != null)

　　　　searchBT(root, "", ans);

        return ans;

    }

    public void searchBT(TreeNode root, String path, List ans) {

        if (root.left == null && root.right == null)

　　　　ans.add(path + root.val);

        if (root.left != null)

　　　　searchBT(root.left, path + root.val + "->", ans);

        if (root.right != null)

　　　　searchBT(root.right, path + root.val + "->", ans);

    }

}

Solution2: //BFS

class Solution {

    public List<String> binaryTreePaths(TreeNode root) {

        List<String> list = new ArrayList<>();

        Stack<TreeNode> sNode=new Stack<>();

        Stack<String> sStr=new Stack<>();

    

        if(root==null) 

            return list;

        sNode.push(root);

        sStr.push("");

        while(!sNode.isEmpty()) {

            TreeNode curNode = sNode.pop();

            String curStr = sStr.pop();

        

            if(curNode.left == null && curNode.right == null) 

                list.add(curStr + curNode.val);

            if(curNode.left != null) {

                sNode.push(curNode.left);

                sStr.push(curStr + curNode.val + "->");

            }

            if(curNode.right != null) {

                sNode.push(curNode.right);

                sStr.push(curStr + curNode.val + "->");

            }

       }

       return list;

    }

}