diff --git a/recursion_dynamic/n_pairs_parentheses/n_pairs_parentheses_challenge.ipynb b/recursion_dynamic/n_pairs_parentheses/n_pairs_parentheses_challenge.ipynb
new file mode 100644
index 0000000..ec4abf3
--- /dev/null
+++ b/recursion_dynamic/n_pairs_parentheses/n_pairs_parentheses_challenge.ipynb
@@ -0,0 +1,162 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<small><i>This notebook was prepared by [Rishi Rajasekaran](https://github.com/rishihot55). Source and license info is available on [Github](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Challenge Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Print all valid combinations of n-pairs of parentheses\n",
+    "\n",
+    "* [Constraints](#Constraints)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm](#Algorithm)\n",
+    "* [Code](#Code)\n",
+    "* [Unit Test](#Unit-Test)\n",
+    "* [Solution Notebook](#Solution-Notebook)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Constraints\n",
+    "* None"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* 0 -> []\n",
+    "* 1 -> [()]\n",
+    "* 2 -> [(()), ()()]\n",
+    "* 3 -> [((())), (()()), (())(), ()(()), ()()()]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "def parentheses_util(no_left, no_right, pair_string, result):\n",
+    "    # TODO: implement parentheses pairing here\n",
+    "    pass\n",
+    "\n",
+    "\n",
+    "def pair_parentheses(n):\n",
+    "    result_set = set()\n",
+    "    if n == 0:\n",
+    "        return result_set\n",
+    "    parentheses_util(n, n, '', result_set)\n",
+    "    return result_set\n"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "ename": "AssertionError",
+     "evalue": "Items in the second set but not the first:\n'()'",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[1;31mAssertionError\u001b[0m                            Traceback (most recent call last)",
+      "\u001b[1;32m<ipython-input-2-11484e8ba6e9>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m     16\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     17\u001b[0m \u001b[1;32mif\u001b[0m \u001b[0m__name__\u001b[0m \u001b[1;33m==\u001b[0m \u001b[1;34m'__main__'\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 18\u001b[1;33m     \u001b[0mmain\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
+      "\u001b[1;32m<ipython-input-2-11484e8ba6e9>\u001b[0m in \u001b[0;36mmain\u001b[1;34m()\u001b[0m\n\u001b[0;32m     13\u001b[0m \u001b[1;32mdef\u001b[0m \u001b[0mmain\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     14\u001b[0m     \u001b[0mtest\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mTestPairParentheses\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 15\u001b[1;33m     \u001b[0mtest\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mtest_pair_parentheses\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mpair_parentheses\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m     16\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     17\u001b[0m \u001b[1;32mif\u001b[0m \u001b[0m__name__\u001b[0m \u001b[1;33m==\u001b[0m \u001b[1;34m'__main__'\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
+      "\u001b[1;32m<ipython-input-2-11484e8ba6e9>\u001b[0m in \u001b[0;36mtest_pair_parentheses\u001b[1;34m(self, solution)\u001b[0m\n\u001b[0;32m      6\u001b[0m     \u001b[1;32mdef\u001b[0m \u001b[0mtest_pair_parentheses\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mself\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0msolution\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      7\u001b[0m         \u001b[0massert_equal\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0msolution\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m0\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mset\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 8\u001b[1;33m         \u001b[0massert_equal\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0msolution\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m1\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mset\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;34m'()'\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m      9\u001b[0m         \u001b[0massert_equal\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0msolution\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m2\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mset\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;34m'(())'\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;34m'()()'\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     10\u001b[0m         \u001b[0massert_equal\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0msolution\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m3\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mset\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;34m'((()))'\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;34m'(()())'\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;34m'(())()'\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;34m'()(())'\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;34m'()()()'\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
+      "\u001b[1;32m/usr/lib/python2.7/unittest/case.py\u001b[0m in \u001b[0;36massertEqual\u001b[1;34m(self, first, second, msg)\u001b[0m\n\u001b[0;32m    511\u001b[0m         \"\"\"\n\u001b[0;32m    512\u001b[0m         \u001b[0massertion_func\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mself\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0m_getAssertEqualityFunc\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mfirst\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0msecond\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m--> 513\u001b[1;33m         \u001b[0massertion_func\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mfirst\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0msecond\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mmsg\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mmsg\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m    514\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m    515\u001b[0m     \u001b[1;32mdef\u001b[0m \u001b[0massertNotEqual\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mself\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mfirst\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0msecond\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mmsg\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mNone\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
+      "\u001b[1;32m/usr/lib/python2.7/unittest/case.py\u001b[0m in \u001b[0;36massertSetEqual\u001b[1;34m(self, set1, set2, msg)\u001b[0m\n\u001b[0;32m    794\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m    795\u001b[0m         \u001b[0mstandardMsg\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m'\\n'\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mjoin\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mlines\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m--> 796\u001b[1;33m         \u001b[0mself\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mfail\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mself\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0m_formatMessage\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mmsg\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mstandardMsg\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m    797\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m    798\u001b[0m     \u001b[1;32mdef\u001b[0m \u001b[0massertIn\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mself\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mmember\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mcontainer\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mmsg\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mNone\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
+      "\u001b[1;32m/usr/lib/python2.7/unittest/case.py\u001b[0m in \u001b[0;36mfail\u001b[1;34m(self, msg)\u001b[0m\n\u001b[0;32m    408\u001b[0m     \u001b[1;32mdef\u001b[0m \u001b[0mfail\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mself\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mmsg\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mNone\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m    409\u001b[0m         \u001b[1;34m\"\"\"Fail immediately, with the given message.\"\"\"\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m--> 410\u001b[1;33m         \u001b[1;32mraise\u001b[0m \u001b[0mself\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mfailureException\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mmsg\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m    411\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m    412\u001b[0m     \u001b[1;32mdef\u001b[0m \u001b[0massertFalse\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mself\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mexpr\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mmsg\u001b[0m\u001b[1;33m=\u001b[0m\u001b[0mNone\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
+      "\u001b[1;31mAssertionError\u001b[0m: Items in the second set but not the first:\n'()'"
+     ]
+    }
+   ],
+   "source": [
+    "# %load test_n_pairs_parentheses.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "class TestPairParentheses(object):\n",
+    "    \n",
+    "    def test_pair_parentheses(self, solution):\n",
+    "        assert_equal(solution(0), set([]))\n",
+    "        assert_equal(solution(1), set(['()']))\n",
+    "        assert_equal(solution(2), set(['(())', '()()']))\n",
+    "        assert_equal(solution(3), set(['((()))','(()())', '(())()', '()(())', '()()()']))\n",
+    "        print('Success: test_pair_parentheses')\n",
+    "\n",
+    "def main():\n",
+    "    test = TestPairParentheses()\n",
+    "    test.test_pair_parentheses(pair_parentheses)\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    main()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Solution Notebook\n",
+    "\n",
+    "Review the [Solution Notebook](#) for a discussion on algorithms and code solutions."
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.9"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/recursion_dynamic/n_pairs_parentheses/n_pairs_parentheses_solution.ipynb b/recursion_dynamic/n_pairs_parentheses/n_pairs_parentheses_solution.ipynb
new file mode 100644
index 0000000..9cdb79e
--- /dev/null
+++ b/recursion_dynamic/n_pairs_parentheses/n_pairs_parentheses_solution.ipynb
@@ -0,0 +1,162 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<small><i>This notebook was prepared by [Rishi Rajasekaran](https://github.com/rishihot55). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Solution Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Print all valid combinations of n-pairs of parentheses\n",
+    "\n",
+    "* [Constraints](#Constraints)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm](#Algorithm)\n",
+    "* [Code](#Code)\n",
+    "* [Unit Test](#Unit-Test)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Constraints\n",
+    "* None"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* 0 -> ''\n",
+    "* 1 -> ()\n",
+    "* 2 -> (()), ()()\n",
+    "* 3 -> ((())), (()()), (())(), ()(()), ()()()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Algorithm\n",
+    "* If no_of_left == 0 and no_of right == 0, add pair_string to result\n",
+    "* Else \n",
+    "    * If (no_left > 0), parentheses_util(no_left - 1, no_right, pair_string + '(', result)\n",
+    "    * If (no_right > no_left), parentheses_util(no_left, no_right - 1, pair_string + ')', result)\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(4^n/n^(3/2)) "
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "def parentheses_util(no_left, no_right, pair_string, result):\n",
+    "    if no_left == 0 and no_right == 0:\n",
+    "        result.add(pair_string)\n",
+    "    else:\n",
+    "        if no_left > 0:\n",
+    "            parentheses_util(no_left - 1, no_right, pair_string + '(', result)\n",
+    "        if no_right > no_left:\n",
+    "            parentheses_util(no_left, no_right - 1, pair_string + ')', result)\n",
+    "\n",
+    "\n",
+    "def pair_parentheses(n):\n",
+    "    result_set = set()\n",
+    "    if n == 0:\n",
+    "        return result_set\n",
+    "    parentheses_util(n, n, '', result_set)\n",
+    "    return result_set\n"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Success: test_pair_parentheses\n"
+     ]
+    }
+   ],
+   "source": [
+    "# %load test_n_pairs_parentheses.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "class TestPairParentheses(object):\n",
+    "    \n",
+    "    def test_pair_parentheses(self, solution):\n",
+    "        assert_equal(solution(0), set([]))\n",
+    "        assert_equal(solution(1), set(['()']))\n",
+    "        assert_equal(solution(2), set(['(())', '()()']))\n",
+    "        assert_equal(solution(3), set(['((()))','(()())', '(())()', '()(())', '()()()']))\n",
+    "        print('Success: test_pair_parentheses')\n",
+    "\n",
+    "def main():\n",
+    "    test = TestPairParentheses()\n",
+    "    test.test_pair_parentheses(pair_parentheses)\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    main()"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.9"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/recursion_dynamic/n_pairs_parentheses/test_n_pairs_parentheses.py b/recursion_dynamic/n_pairs_parentheses/test_n_pairs_parentheses.py
new file mode 100644
index 0000000..52d19d7
--- /dev/null
+++ b/recursion_dynamic/n_pairs_parentheses/test_n_pairs_parentheses.py
@@ -0,0 +1,17 @@
+from nose.tools import assert_equal
+
+class TestPairParentheses(object):
+    
+    def test_pair_parentheses(self, solution):
+        assert_equal(solution(0), set([]))
+        assert_equal(solution(1), set(['()']))
+        assert_equal(solution(2), set(['(())', '()()']))
+        assert_equal(solution(3), set(['((()))','(()())', '(())()', '()(())', '()()()']))
+        print('Success: test_pair_parentheses')
+
+def main():
+    test = TestPairParentheses()
+    test.test_pair_parentheses(pair_parentheses)
+
+if __name__ == '__main__':
+    main()
\ No newline at end of file