[feature] add problem

recursion/matrix_maximum_coins.ipynb

@@ -0,0 +1,59 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### Problem \n",
+    "You are given a 2-d matrix where each cell represents number of coins in that cell. Assuming we start at matrix[0][0], and can only move right or down, find the maximum number of coins you can collect by the bottom right corner.\n",
+    "\n",
+    "For example, in this matrix\n",
+    "\n",
+    "```python\n",
+    "0 3 1 1\n",
+    "2 0 0 4\n",
+    "1 5 3 1\n",
+    "```\n",
+    "\n",
+    "The most we can collect is 0 + 2 + 1 + 5 + 3 + 1 = 12 coins."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def collect_coins(matrix, r=0, c=0, cache=None):\n",
+    "    if cache is None:\n",
+    "        cache = {}\n",
+    "    \n",
+    "    is_bottom = matrix[]\n",
+    "    is_rightmost = matrix[-1][-1]\n",
+    "    if (r, c) not in cache:\n",
+    "        if cache[r][c]"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.7.6"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}