{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 63,
   "metadata": {},
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   "source": [
    "# The main function that prints  \n",
    "# all combinations of size r in  \n",
    "# arr[] of size n. This function  \n",
    "# mainly uses combinationUtil() \n",
    "def printCombination(arr, n, r): \n",
    "      \n",
    "    # A temporary array to  \n",
    "    # store all combination \n",
    "    # one by one \n",
    "    data = [0]*r; \n",
    "  \n",
    "    # Print all combination  \n",
    "    # using temprary array 'data[]' \n",
    "    combinationUtil(arr, data, 0,  \n",
    "                    n - 1, 0, r); \n",
    "  \n",
    "# arr[] ---> Input Array \n",
    "# data[] ---> Temporary array to \n",
    "#         store current combination \n",
    "# start & end ---> Staring and Ending \n",
    "#             indexes in arr[] \n",
    "# index ---> Current index in data[] \n",
    "# r ---> Size of a combination  \n",
    "# to be printed  \n",
    "def combinationUtil(arr, data, start,  \n",
    "                    end, index, r): \n",
    "                          \n",
    "    temp1 =[]\n",
    "    # Current combination is ready  \n",
    "    # to be printed, print it \n",
    "    if (index == r): \n",
    "        temp2 = []\n",
    "        for j in range(r): \n",
    "            temp2.append(data[j])\n",
    "            #print(data[j], end = \" \"); \n",
    "        #print(); \n",
    "        #temp1.append(temp2)\n",
    "        #return temp1\n",
    "    \n",
    "    # replace index with all \n",
    "    # possible elements. The \n",
    "    # condition \"end-i+1 >=  \n",
    "    # r-index\" makes sure that  \n",
    "    # including one element at \n",
    "    # index will make a combination  \n",
    "    # with remaining elements at  \n",
    "    # remaining positions \n",
    "    i = start;  \n",
    "    while(i <= end and end - i + 1 >= r - index): \n",
    "        data[index] = arr[i]; \n",
    "        combinationUtil(arr, data, i + 1,  \n",
    "                        end, index + 1, r); \n",
    "        i += 1; \n",
    "        \n",
    "    return temp1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 64,
   "metadata": {},
   "outputs": [
    {
     "ename": "IndexError",
     "evalue": "list assignment index out of range",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mIndexError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-64-eede45e736f3>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      3\u001b[0m \u001b[0mn\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mlen\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0marr\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      4\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 5\u001b[0;31m \u001b[0malg\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mprintCombination\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0marr\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0mn\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;36m3\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-63-85ad8d7a3f5f>\u001b[0m in \u001b[0;36mprintCombination\u001b[0;34m(arr, n, r)\u001b[0m\n\u001b[1;32m     13\u001b[0m     \u001b[0;31m# using temprary array 'data[]'\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     14\u001b[0m     combinationUtil(arr, data, 0,  \n\u001b[0;32m---> 15\u001b[0;31m                     n - 1, 0, r); \n\u001b[0m\u001b[1;32m     16\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     17\u001b[0m \u001b[0;31m# arr[] ---> Input Array\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-63-85ad8d7a3f5f>\u001b[0m in \u001b[0;36mcombinationUtil\u001b[0;34m(arr, data, start, end, index, r)\u001b[0m\n\u001b[1;32m     50\u001b[0m         \u001b[0mdata\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mindex\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0marr\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mi\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m;\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     51\u001b[0m         combinationUtil(arr, data, i + 1,  \n\u001b[0;32m---> 52\u001b[0;31m                         end, index + 1, r); \n\u001b[0m\u001b[1;32m     53\u001b[0m         \u001b[0mi\u001b[0m \u001b[0;34m+=\u001b[0m \u001b[0;36m1\u001b[0m\u001b[0;34m;\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     54\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-63-85ad8d7a3f5f>\u001b[0m in \u001b[0;36mcombinationUtil\u001b[0;34m(arr, data, start, end, index, r)\u001b[0m\n\u001b[1;32m     50\u001b[0m         \u001b[0mdata\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mindex\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0marr\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mi\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m;\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     51\u001b[0m         combinationUtil(arr, data, i + 1,  \n\u001b[0;32m---> 52\u001b[0;31m                         end, index + 1, r); \n\u001b[0m\u001b[1;32m     53\u001b[0m         \u001b[0mi\u001b[0m \u001b[0;34m+=\u001b[0m \u001b[0;36m1\u001b[0m\u001b[0;34m;\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     54\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-63-85ad8d7a3f5f>\u001b[0m in \u001b[0;36mcombinationUtil\u001b[0;34m(arr, data, start, end, index, r)\u001b[0m\n\u001b[1;32m     50\u001b[0m         \u001b[0mdata\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mindex\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0marr\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mi\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m;\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     51\u001b[0m         combinationUtil(arr, data, i + 1,  \n\u001b[0;32m---> 52\u001b[0;31m                         end, index + 1, r); \n\u001b[0m\u001b[1;32m     53\u001b[0m         \u001b[0mi\u001b[0m \u001b[0;34m+=\u001b[0m \u001b[0;36m1\u001b[0m\u001b[0;34m;\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     54\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-63-85ad8d7a3f5f>\u001b[0m in \u001b[0;36mcombinationUtil\u001b[0;34m(arr, data, start, end, index, r)\u001b[0m\n\u001b[1;32m     48\u001b[0m     \u001b[0mi\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mstart\u001b[0m\u001b[0;34m;\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     49\u001b[0m     \u001b[0;32mwhile\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mi\u001b[0m \u001b[0;34m<=\u001b[0m \u001b[0mend\u001b[0m \u001b[0;32mand\u001b[0m \u001b[0mend\u001b[0m \u001b[0;34m-\u001b[0m \u001b[0mi\u001b[0m \u001b[0;34m+\u001b[0m \u001b[0;36m1\u001b[0m \u001b[0;34m>=\u001b[0m \u001b[0mr\u001b[0m \u001b[0;34m-\u001b[0m \u001b[0mindex\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 50\u001b[0;31m         \u001b[0mdata\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mindex\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0marr\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mi\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m;\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m     51\u001b[0m         combinationUtil(arr, data, i + 1,  \n\u001b[1;32m     52\u001b[0m                         end, index + 1, r); \n",
      "\u001b[0;31mIndexError\u001b[0m: list assignment index out of range"
     ]
    }
   ],
   "source": [
    "arr =[1,3,5,7,9,11,13,15]\n",
    "\n",
    "n = len(arr)\n",
    "\n",
    "alg = printCombination(arr,n,3)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 62,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "None\n"
     ]
    }
   ],
   "source": [
    "print(alg)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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