257.二叉树的所有路径

方法：深度优先搜索

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public List<String> binaryTreePaths(TreeNode root) {List<String> ans = new ArrayList<>();StringBuilder sb = new StringBuilder();dfs(root,ans,sb);return ans;}public void dfs(TreeNode root,List<String> paths,StringBuilder s){if(root == null){return;} s.append(root.val);if(root.left == null && root.right == null){paths.add(s.toString());return;}dfs(root.left,paths,new StringBuilder(s).append("->"));dfs(root.right,paths,new StringBuilder(s).append("->"));}
}