# 257 Binary Tree Paths

給一棵Binary Tree，印出所有root-leaf paths

• Idea: 蠻單純的，recursive dfs

• Code:

  /**
   * Definition for a binary tree node.
   * public class TreeNode {
   *     int val;
   *     TreeNode left;
   *     TreeNode right;
   *     TreeNode(int x) { val = x; }
   * }
   */
  public class Solution {
      List<String> res = new ArrayList<>();
      public List<String> binaryTreePaths(TreeNode root) {
          /*
          dfs each branch(stack), record as string
          */
          if(root == null) return res;
          int val = root.val;
          dfs(root, ""+val);
          return res;
      }
  
      void dfs(TreeNode n, String s){
          if(n.right == null && n.left == null){
              res.add(s);
              return;
          }
          if(n.right != null) dfs(n.right, s+"->"+n.right.val);
          if(n.left != null) dfs(n.left, s+"->"+n.left.val);
      }
  
  }