import java.util.ArrayList;

import java.util.HashSet;

import java.util.List;

import java.util.Set;

/**

* created by zl on 2019/3/29 8:03

*/

public class simple_257_BinaryTreePaths

{

public List<String> binaryTreePaths(TreeNode root)

{

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

if(root == null)

return list;

StringBuilder sb = new StringBuilder();

core(sb,root,list);

return list;

}

private void core(StringBuilder sb , TreeNode root,List<String> list)

{

if(root == null)

return ;

if(sb.length() != 0)

{

sb.append("->");

sb.append(root.val);

}else

{

sb.append(root.val);

}

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

{

list.add(sb.toString());

return ;

}

StringBuilder newSb = new StringBuilder(sb.toString());//深拷贝代替回溯

core(sb,root.left, list);

core(newSb, root.right, list);

}

}