From caafed6c1ef8ac75c52456a44992f4fa243f11d7 Mon Sep 17 00:00:00 2001
From: Shahrear Bin Amin <shahrearbinamin1@gmail.com>
Date: Thu, 5 Jan 2023 18:50:16 +0600
Subject: [PATCH 1/2] added Unique Binary Search Tree with dynamic programming

---
 .../unique_binary_search_tree.dart            | 34 +++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 dynamic_programming/unique_binary_search_tree.dart

diff --git a/dynamic_programming/unique_binary_search_tree.dart b/dynamic_programming/unique_binary_search_tree.dart
new file mode 100644
index 0000000..784fa06
--- /dev/null
+++ b/dynamic_programming/unique_binary_search_tree.dart
@@ -0,0 +1,34 @@
+import 'package:test/test.dart';
+
+// Problem - https://leetcode.com/problems/unique-binary-search-trees/description/
+// Given an integer n, return the number of structurally unique BST's (binary search trees)
+// which has exactly n nodes of unique values from 1 to n.
+
+class UniqueBST {
+  int solve(int i, List<int> dp) {
+    if (i == 0 || i == 1) return 1;
+    if (dp[i] != -1) return dp[i];
+
+    int total = 0;
+    for (int k = 1; k <= i; k++) {
+      total += solve(k - 1, dp) * solve(i - k, dp);
+    }
+    return dp[i] = total;
+  }
+
+  int numTrees(int n) {
+    List<int> dp = List.filled(20, -1);
+    return this.solve(n, dp);
+  }
+}
+
+void main() {
+  var uniqueBST = UniqueBST();
+  test('Test Case 1: Input 3, Output - 5', () {
+    expect(uniqueBST.numTrees(3), 5);
+  });
+
+  test('Test Case 2: Input 1, Output - 1', () {
+    expect(uniqueBST.numTrees(1), 1);
+  });
+}

From b71b6906d659df1849376f1f1b7591d3199f0bb0 Mon Sep 17 00:00:00 2001
From: Shahrear Bin Amin <shahrearbinamin1@gmail.com>
Date: Thu, 5 Jan 2023 20:08:33 +0600
Subject: [PATCH 2/2] removed hardcoded List dp length

---
 dynamic_programming/unique_binary_search_tree.dart | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dynamic_programming/unique_binary_search_tree.dart b/dynamic_programming/unique_binary_search_tree.dart
index 784fa06..ee5b3a9 100644
--- a/dynamic_programming/unique_binary_search_tree.dart
+++ b/dynamic_programming/unique_binary_search_tree.dart
@@ -17,7 +17,7 @@ class UniqueBST {
   }
 
   int numTrees(int n) {
-    List<int> dp = List.filled(20, -1);
+    List<int> dp = List.filled(n + 1, -1);
     return this.solve(n, dp);
   }
 }