Create solution2.ipynb

Author: alesanchezr

notebook/solution2.ipynb

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+{
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+{
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+"# Algorithm Optimization problems"
+]
+},
+{
+"cell_type": "markdown",
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+"source": [
+"## Exercise 2 : QuickSort algorithm\n",
+"\n",
+"Quicksort is a naturally recursive algorithm - divide the input array into smaller arrays, move the elements to the proper side of the pivot, and repeat. \n",
+"\n",
+"When we first call the algorithm, we consider all of the elements - from indexes **0** to **n-1** where **n** is the number of elements in our array. If our pivot ended up in position **k**, we'd then repeat the process for elements from **0 to k-1** and from **k+1** to **n-1**.\n",
+"\n",
+"This time we are going to order an array by using two functions - partition() and quick_sort(). The quick_sort() function will first partition() the collection and then recursively call itself on the divided parts.\n",
+"\n",
+"The code for the partition() function has been provided to you in the following cell. Use this partition() function to implement the quick_sort() function in order to sort the following array:\n",
+"\n",
+"array = [29,99,23,41,66,28,44,78,87,19,31,76,58,88,82,97,12,21,44]"
+]
+},
+{
+"cell_type": "code",
+"execution_count": null,
+"id": "e32eceef",
+"metadata": {},
+"outputs": [],
+"source": [
+"def partition(array, start, end):\n",
+"    pivot = array[start]\n",
+"    low = start + 1\n",
+"    high = end\n",
+"\n",
+"    while True:\n",
+"        # If the current value we're looking at is larger than the pivot\n",
+"        # it's in the right place (right side of pivot) and we can move left,\n",
+"        # to the next element.\n",
+"        # We also need to make sure we haven't surpassed the low pointer, since that\n",
+"        # indicates we have already moved all the elements to their correct side of the pivot\n",
+"        while low <= high and array[high] >= pivot:\n",
+"            high = high - 1\n",
+"\n",
+"        # Opposite process of the one above\n",
+"        while low <= high and array[low] <= pivot:\n",
+"            low = low + 1\n",
+"\n",
+"        # We either found a value for both high and low that is out of order\n",
+"        # or low is higher than high, in which case we exit the loop\n",
+"        if low <= high:\n",
+"            array[low], array[high] = array[high], array[low]\n",
+"            # The loop continues\n",
+"        else:\n",
+"            # We exit out of the loop\n",
+"            break\n",
+"\n",
+"    array[start], array[high] = array[high], array[start]\n",
+"\n",
+"    return high"
+]
+},
+{
+"cell_type": "code",
+"execution_count": null,
+"id": "c0c22449",
+"metadata": {},
+"outputs": [],
+"source": [
+"def quick_sort(array, start, end):\n",
+"    #COMPLETE HERE THE CODE OF THE quick_sort() ARRAY\n",
+"    if start >= end:\n",
+"        return\n",
+"\n",
+"    p = partition(array, start, end)\n",
+"    quick_sort(array, start, p-1)\n",
+"    quick_sort(array, p+1, end)"
+]
+},
+{
+"cell_type": "code",
+"execution_count": null,
+"id": "e6cd4c0e",
+"metadata": {},
+"outputs": [],
+"source": [
+"#RUN YOUR quick_sort() FUNCTION ON THE GIVEN ARRAY AND PRINT THE RESULT (SORTED ARRAY).\n",
+"\n",
+"array = [29,99,23,41,66,28,44,78,87,19,31,76,58,88,82,97,12,21,44]\n",
+"\n",
+"quick_sort(array, 0, len(array) - 1)\n",
+"print(array)"
+]
+},
+{
+"cell_type": "markdown",
+"id": "b281af6e",
+"metadata": {},
+"source": [
+"Source:\n",
+"\n",
+"https://www.geeksforgeeks.org/\n",
+"\n",
+"https://stackabuse.com/big-o-notation-and-algorithm-analysis-with-python-examples/\n",
+"\n",
+"https://stackabuse.com/quicksort-in-python/\n",
+"\n",
+"https://stackabuse.com/k-nearest-neighbors-algorithm-in-python-and-scikit-learn/"
+]
+}
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