95. Unique Binary Search Trees II (java)

Author: bluesword12350

solution/0095.Unique Binary Search Trees II/Solution.java

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+class Solution {
+    public List<TreeNode> generateTrees(int n) {
+        if (n <= 0) return new ArrayList<>();
+        return generateTrees(1, n);
+    }
+    private List<TreeNode> generateTrees(int left, int right) {
+        List<TreeNode> list = new ArrayList<>();
+        if (left > right) {
+            list.add(null);
+        } else {
+            for (int i = left; i <= right; i++) {
+                List<TreeNode> leftTrees = generateTrees(left, i - 1);
+                List<TreeNode> rightTrees = generateTrees(i + 1, right);
+                for (TreeNode l : leftTrees) {
+                    for (TreeNode r : rightTrees) {
+                        TreeNode root = new TreeNode(i);
+                        root.left = l;
+                        root.right = r;
+                        list.add(root);
+                    }
+                }
+            }
+        }
+        return list;
+    }
+}