solves git add .

Author: anishLearnsToCode

src/GenerateParentheses.java

@@ -0,0 +1,40 @@
+// https://leetcode.com/problems/generate-parentheses
+// T: O(Catalan-number(n)) or O(4^n/sqrt(n))
+// S: O(Catalan-number(n)) or O(4^n/sqrt(n))
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class GenerateParentheses {
+    private static final Map<Integer, List<String>> VALID_PARENTHESES = new HashMap<>();
+
+    static {
+        VALID_PARENTHESES.put(0, List.of(""));
+        VALID_PARENTHESES.put(1, List.of("()"));
+        for (int i = 2 ; i <= 8 ; i++) {
+            addValidParentheses(i);
+        }
+    }
+
+    private static void addValidParentheses(int i) {
+        final List<String> result = new ArrayList<>();
+        addValidParentheses(i, result);
+        VALID_PARENTHESES.put(i, result);
+    }
+
+    private static void addValidParentheses(int i, List<String> result) {
+        for (int k = 0 ; k < i ; k++) {
+            for (String s1 : VALID_PARENTHESES.get(i - k - 1)) {
+                for (String s2 : VALID_PARENTHESES.get(k)) {
+                    result.add("(" + s1 + ")" + s2);
+                }
+            }
+        }
+    }
+
+    public List<String> generateParenthesis(int n) {
+        return VALID_PARENTHESES.get(n);
+    }
+}