Merge pull request #94 from Joshua-Lu/patch-10

更新 0257.二叉树的所有路径 Java版本

problems/0257.二叉树的所有路径.md

@@ -281,39 +281,47 @@ public:
 ## 其他语言版本
 
 Java：
-```java
+
+```Java
 class Solution {
+    /**
+     * 递归法
+     */
     public List<String> binaryTreePaths(TreeNode root) {
-        LinkedList<TreeNode> stack = new LinkedList<>();
-        List<String> list = new LinkedList<>();
-        TreePaths(root,stack,list);
-        return list;
+        List<String> res = new ArrayList<>();
+        if (root == null) {
+            return res;
+        }
+        List<Integer> paths = new ArrayList<>();
+        traversal(root, paths, res);
+        return res;
     }
 
-    private static void TreePaths (TreeNode root, LinkedList<TreeNode> path, List<String> res) {
-        path.add(root);
+    private void traversal(TreeNode root, List<Integer> paths, List<String> res) {
+        paths.add(root.val);
+        // 叶子结点
         if (root.left == null && root.right == null) {
+            // 输出
             StringBuilder sb = new StringBuilder();
-            for (TreeNode n : path) {
-                sb.append(n.val);
-                sb.append("->");
+            for (int i = 0; i < paths.size() - 1; i++) {
+                sb.append(paths.get(i)).append("->");
             }
-            sb.delete(sb.length()-2,sb.length());
+            sb.append(paths.get(paths.size() - 1));
             res.add(sb.toString());
             return;
         }
         if (root.left != null) {
-            TreePaths(root.left, path, res);
-            path.removeLast();
+            traversal(root.left, paths, res);
+            paths.remove(paths.size() - 1);// 回溯
         }
         if (root.right != null) {
-            TreePaths(root.right, path, res);
-            path.removeLast();
+            traversal(root.right, paths, res);
+            paths.remove(paths.size() - 1);// 回溯
         }
     }
 }
-```
 
+```
 
 Python：