Added task 22.

Author: javadev

src/main/java/s0022.generate.parentheses/Solution.java

@@ -0,0 +1,35 @@
+package s0022.generate.parentheses;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Solution {
+
+    public List<String> generate(StringBuilder sb, List<String> str, int open, int close) {
+
+        if (open == 0 && close == 0) {
+            str.add(sb.toString());
+            return str;
+        }
+
+        if (open > 0) {
+            sb.append('(');
+            generate(sb, str, open - 1, close);
+            sb.deleteCharAt(sb.length() - 1);
+        }
+        if (close > 0) {
+            if (open < close) {
+                sb.append(')');
+                generate(sb, str, open, close - 1);
+                sb.deleteCharAt(sb.length() - 1);
+            }
+        }
+        return str;
+    }
+
+    public List<String> generateParenthesis(int n) {
+        StringBuilder sb = new StringBuilder();
+        List<String> ans = new ArrayList<>();
+        return generate(sb, ans, n, n);
+    }
+}

src/test/java/s0022.generate.parentheses/SolutionTest.java

@@ -0,0 +1,15 @@
+package s0022.generate.parentheses;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.Test;
+
+public class SolutionTest {
+    @Test
+    public void generateParenthesis() {
+        assertThat(
+                new Solution().generateParenthesis(3).toString(),
+                equalTo("[((())), (()()), (())(), ()(()), ()()()]"));
+    }
+}