binary tree paths

Author: fishercoder1534

Common/src/utils/CommonUtils.java

@@ -132,4 +132,12 @@ public static void printMatrix(int[][] matrix) {
         System.out.println("----------------------------------------------------");
     }
 
+    public static void print(List<String> list) {
+        System.out.println("----------------------------------------------------");
+        for(String str : list){
+            System.out.print(str + ", ");
+        }
+        System.out.println();
+    }
+
 }

EASY/src/easy/BinaryTreePaths.java

@@ -0,0 +1,75 @@
+package easy;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import utils.CommonUtils;
+import classes.TreeNode;
+
+/**257. Binary Tree Paths  Question Editorial Solution  My Submissions
+Total Accepted: 59117
+Total Submissions: 191659
+Difficulty: Easy
+Given a binary tree, return all root-to-leaf paths.
+
+For example, given the following binary tree:
+
+   1
+ /   \
+2     3
+ \
+  5
+All root-to-leaf paths are:
+
+["1->2->5", "1->3"]
+*/
+public class BinaryTreePaths {
+    //a very typical/good question to test your recursion/dfs understanding.
+    public List<String> binaryTreePaths_more_concise(TreeNode root) {
+        List<String> paths = new ArrayList<String>();
+        if(root == null) return paths;
+        dfs(root, paths, "");
+        return paths;
+    }
+    
+    private void dfs(TreeNode root, List<String> paths, String path) {
+        if(root.left == null && root.right == null){
+            paths.add(path + root.val);
+            return;
+        }
+        path += root.val + "->";
+        if(root.left != null) dfs(root.left, paths, path);
+        if(root.right != null) dfs(root.right, paths, path);
+    }
+    
+    public static void main(String...strings){
+        BinaryTreePaths test = new BinaryTreePaths();
+        TreeNode root = new TreeNode(1);
+        root.left = new TreeNode(2);
+        root.left.right = new TreeNode(5);
+        root.right = new TreeNode(3);
+        List<String> res = test.binaryTreePaths(root);
+        CommonUtils.print(res);
+    }
+
+    public List<String> binaryTreePaths(TreeNode root) {
+        List<String> paths = new ArrayList<String>();
+        dfs(root, paths, new StringBuilder());
+        return paths;
+    }
+
+    private void dfs(TreeNode root, List<String> paths, StringBuilder sb) {
+        if(root == null) return;
+        if(root.left == null && root.right == null){
+          sb.append(root.val);
+          paths.add(sb.toString());
+          return ;
+        } 
+        sb.append(root.val + "->");
+        String curr = sb.toString();
+        if(root.left != null) dfs(root.left, paths, sb);
+        sb.setLength(0);
+        sb.append(curr);
+        if(root.right != null) dfs(root.right, paths, sb);
+    }
+}