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"]
题目含义：找到所有从根到叶子加点的路径

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