Chapter 07 section 04 C++ codes updated. Java codes added.

Author: liuyubobobo

07-Binary-Tree-and-Recursion/Course Code (C++)/04-Binary-Tree-Paths/main.cpp

@@ -4,6 +4,12 @@
 
 using namespace std;
 
+
+/// 257. Binary Tree Paths
+/// https://leetcode.com/problems/binary-tree-paths/description/
+/// 时间复杂度: O(n), n为树中的节点个数
+/// 空间复杂度: O(h), h为树的高度
+
 /// Definition for a binary tree node.
 struct TreeNode {
     int val;
@@ -18,21 +24,21 @@ class Solution {
 
         vector<string> res;
 
-        if( root == NULL )
+        if(root == NULL)
             return res;
 
-        if( root->left == NULL && root->right == NULL ){
-            res.push_back( to_string(root->val) );
+        if(root->left == NULL && root->right == NULL){
+            res.push_back(to_string(root->val));
             return res;
         }
 
         vector<string> leftPaths = binaryTreePaths(root->left);
-        for( int i = 0 ; i < leftPaths.size() ; i ++ )
-            res.push_back( to_string(root->val) + "->" + leftPaths[i] );
+        for(int i = 0 ; i < leftPaths.size() ; i ++)
+            res.push_back(to_string(root->val) + "->" + leftPaths[i]);
 
         vector<string> rightPaths = binaryTreePaths(root->right);
-        for( int i = 0 ; i < rightPaths.size() ; i ++ )
-            res.push_back( to_string(root->val) + "->" + rightPaths[i] );
+        for(int i = 0 ; i < rightPaths.size() ; i ++)
+            res.push_back(to_string(root->val) + "->" + rightPaths[i]);
 
         return res;
     }

07-Binary-Tree-and-Recursion/Course Code (Java)/04-Binary-Tree-Paths/src/Solution.java

@@ -0,0 +1,48 @@
+import java.util.List;
+import java.util.ArrayList;
+
+/// 257. Binary Tree Paths
+/// https://leetcode.com/problems/binary-tree-paths/description/
+/// 时间复杂度: O(n), n为树中的节点个数
+/// 空间复杂度: O(h), h为树的高度
+public class Solution {
+
+    // Definition for a binary tree node.
+    public class TreeNode {
+        int val;
+        TreeNode left;
+        TreeNode right;
+        TreeNode(int x) { val = x; }
+    }
+
+    public List<String> binaryTreePaths(TreeNode root) {
+
+        ArrayList<String> res = new ArrayList<String>();
+
+        if(root == null)
+            return res;
+
+        if(root.left == null && root.right == null){
+            res.add(Integer.toString(root.val));
+            return res;
+        }
+
+        List<String> leftPaths = binaryTreePaths(root.left);
+        for(String s: leftPaths){
+            StringBuilder sb = new StringBuilder(Integer.toString(root.val));
+            sb.append("->");
+            sb.append(s);
+            res.add(sb.toString());
+        }
+
+        List<String> rightPaths = binaryTreePaths(root.right);
+        for(String s: rightPaths) {
+            StringBuilder sb = new StringBuilder(Integer.toString(root.val));
+            sb.append("->");
+            sb.append(s);
+            res.add(sb.toString());
+        }
+
+        return res;
+    }
+}