From 59403e05819e659dd3a0566656774bc6dd48846e Mon Sep 17 00:00:00 2001
From: KailokFung <jialuo_feng@foxmail.com>
Date: Sat, 3 Jul 2021 16:14:10 +0800
Subject: [PATCH] =?UTF-8?q?feat(0257):=20=E6=96=B0=E5=A2=9E=E4=B8=A4?=
 =?UTF-8?q?=E7=A7=8Djava=E8=A7=A3=E6=B3=95?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problems/0257.二叉树的所有路径.md | 49 ++++++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/problems/0257.二叉树的所有路径.md b/problems/0257.二叉树的所有路径.md
index d5a0478e..ce596396 100644
--- a/problems/0257.二叉树的所有路径.md
+++ b/problems/0257.二叉树的所有路径.md
@@ -283,6 +283,7 @@ public:
 Java：
 
 ```Java
+//解法一
 class Solution {
     /**
      * 递归法
@@ -321,6 +322,52 @@ class Solution {
     }
 }
 
+//解法二（常规前序遍历，不用回溯），更容易理解
+class Solution {
+    public List<String> binaryTreePaths(TreeNode root) {
+        List<String> res = new ArrayList<>();
+        helper(root, new StringBuilder(), res);
+        return res;
+    }
+
+    public void helper(TreeNode root, StringBuilder sb, List<String> res) {
+        if (root == null) {return;}
+      	// 遇到叶子结点就放入当前路径到res集合中
+        if (root.left == null && root.right ==null) {
+            sb.append(root.val);
+            res.add(sb.toString());
+          	// 记得结束当前方法
+            return;
+        }
+        helper(root.left,new StringBuilder(sb).append(root.val + "->"),res);
+        helper(root.right,new StringBuilder(sb).append(root.val + "->"),res);
+    }
+}
+
+//针对解法二优化，思路本质是一样的
+class Solution {
+    public List<String> binaryTreePaths(TreeNode root) {
+        List<String> res = new ArrayList<>();
+        helper(root, "", res);
+        return res;
+    }
+
+    public void helper(TreeNode root, String path, List<String> res) {
+        if (root == null) {return;}
+      	// 由原始解法二可以知道，root的值肯定会下面某一个条件加入到path中，那么干脆直接在这一步加入即可
+        StringBuilder sb = new StringBuilder(path);
+        sb.append(root.val);
+        if (root.left == null && root.right ==null) {
+            res.add(sb.toString());
+        }else{
+          	// 如果是非叶子结点则还需要跟上一个 “->”
+            sb.append("->");
+            helper(root.left,sb.toString(),res);
+            helper(root.right,sb.toString(),res);
+        }
+    }
+}
+
 ```
 
 Python：
@@ -350,7 +397,7 @@ class Solution:
 
 ```
 Go：
-  
+
 ```go
 func binaryTreePaths(root *TreeNode) []string {
     res := make([]string, 0)