add 096

Author: shishishu

README.md

@@ -36,4 +36,5 @@ Idx | Date | Question | Python| Java | Domain | Tag | Difficulty | Remark
 030|20200329|[1. Two Sum](https://leetcode.com/problems/two-sum/)|[001p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/001_Two_Sum.ipynb)|[001j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/001/Solution.java)|Array|HashTable|Easy
 031|20200329|[653. Two Sum IV - Input is a BST](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/)|[653p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/653_Two_Sum_IV_-_Input_is_a_BST.ipynb)|[653j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/653/Solution.java)|BST| |Easy
 032|20200406|[226. Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/)|[226p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/226_Invert_Binary_Tree.ipynb)|[226j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/226/Solution.java)|Tree|Recursive/Iterative|Easy
-033|20200406|[110. Balanced Binary Tree](https://leetcode.com/problems/balanced-binary-tree/)|[110p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/110_Balanced_Binary_Tree.ipynb)|[110j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/110/Solution.java)|Tree|Recursive|Easy
+033|20200406|[110. Balanced Binary Tree](https://leetcode.com/problems/balanced-binary-tree/)|[110p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/110_Balanced_Binary_Tree.ipynb)|[110j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/110/Solution.java)|Tree|Recursive|Easy
+034|20200406|[96. Unique Binary Search Trees](https://leetcode.com/problems/unique-binary-search-trees/)|[096p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/096_Unique_Binary_Search_Trees.ipynb)|[096j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/096/Solution.java)|BST|DP|Medium

images/096_Q.PNG

@@ -0,0 +1,30 @@
+// DP
+class Solution {
+    public int numTrees(int n) {
+        int[] G = new int[n + 1];
+        G[0] = G[1] = 1;
+        for (int i=2; i <= n; i++){
+            for (int j=1; j<=i; j++){
+                G[i] += G[j - 1] * G[i - j];
+            }
+        }
+        return G[n];
+    }
+}
+
+// Recursive
+class Solution {
+    public int numTrees(int n) {
+        return subTrees(1, n);
+    }
+    public int subTrees(int lo, int hi){
+        if (lo >= hi){
+            return 1;
+        }
+        int total = 0;
+        for (int i=lo; i<=hi; i++){
+            total += subTrees(lo, i - 1) * subTrees(i + 1, hi);
+        }
+        return total;
+    }
+}

images/096_S1.PNG

@@ -37,6 +37,7 @@
       <sourceFolder url="file://$MODULE_DIR$/653" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/226" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/110" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/096" isTestSource="false" />
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />