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"]

class Solution {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> answer = new ArrayList<String>();
        if(root!=null) serBST(root,"",answer);
        return answer;
    }
    private void serBST(TreeNode root,String path,List<String> answer){
        if(root.left==null && root.right==null) answer.add(path+root.val);
        if(root.left!=null)   serBST(root.left,path+root.val+"->",answer);
        if(root.right!=null) serBST(root.right,path+root.val+"->",answer);
    }
}