feat: implements pre course exercises

Exercise_1.py

@@ -1,22 +1,37 @@
 # Python code to implement iterative Binary  
 # Search. 
 
-# It returns location of x in given array arr  
+# It returns location of target in given array arr  
 # if present, else returns -1 
-def binarySearch(arr, l, r, x): 
-
+'''
+arr = [2 3 5 [10] {40}]
+left = 3
+right = 4
+middle = 3
+target = 10
+'''
+def binarySearch(arr, left, right, target): 
   #write your code here
-
-
+  while left <= right:
+    middle = (left + right) // 2
+
+    if arr[middle] == target:
+       return middle
+    elif arr[middle] < target:
+       left = middle + 1
+    else:
+       right = middle - 1
+
+  return - 1
 
 # Test array 
 arr = [ 2, 3, 4, 10, 40 ] 
-x = 10
+target = 10
 
 # Function call 
-result = binarySearch(arr, 0, len(arr)-1, x) 
+result = binarySearch(arr, 0, len(arr) - 1, target) 
 
 if result != -1: 
-    print "Element is present at index % d" % result 
+    print("Element is present at index % d" % result)
 else: 
-    print "Element is not present in array"
+    print("Element is not present in array")

Exercise_2.py

@@ -1,16 +1,35 @@
 # Python program for implementation of Quicksort Sort 
 
 # give you explanation for the approach
-def partition(arr,low,high):
-
+'''
+There are a lot of partitions that I could possibly use. The most efficient partition I understand easily is the Lomuto partition.
+
+I recognize that Hoare's partition is the fastest of all, but I have stuck with what I understand for now
+
+Basically as I understand it we keep track of the smaller element relative to the pivot and keep moving them left. Once we're done we swap the pivot into it's appropriate position,
+and all elements less than it will be to the left and all elements to the right will be greater. We then keep doing this recursively until we've processed the entire array
+'''
+def partition(arr, low, high):
+    pivot = arr[high]
+    smallerIndex = low - 1
+
+    for index in range(low, high):
+        # Move all smaller elements to the left side
+        if arr[index] < pivot:
+            smallerIndex += 1
+            arr[smallerIndex], arr[index] = arr[index], arr[smallerIndex]
+
+    arr[smallerIndex + 1], arr[high] = arr[high], arr[smallerIndex + 1]
 
-    #write your code here
+    return smallerIndex + 1
 
 
 # Function to do Quick sort 
-def quickSort(arr,low,high): 
-
-    #write your code here
+def quickSort(arr, low, high): 
+    if low < high:
+        pivotIndex = partition(arr, low, high)
+        quickSort(arr, low, pivotIndex - 1)
+        quickSort(arr, pivotIndex + 1, high)    
 
 # Driver code to test above 
 arr = [10, 7, 8, 9, 1, 5] 

Exercise_3.py

@@ -1,20 +1,38 @@
 # Node class  
 class Node:  
-
-    # Function to initialise the node object  
     def __init__(self, data):  
+        self.data = data
+        self.next = None
 
-class LinkedList: 
-
+class LinkedList:   
     def __init__(self): 
-
+        self.head = None
+        self.tail = None
+        self.length = 0
 
     def push(self, new_data): 
-
+        new_node = Node(new_data)
+        #  Edge cases, we add our first new_node
+        is_first_node = self.length == 0
+        self.length += 1
+
+        if is_first_node:
+            self.head = new_node
+            self.tail = new_node
+            return
+
+        # Otherwise it is very standard
+        self.tail.next = new_node
+        self.tail = new_node
 
-    # Function to get the middle of  
-    # the linked list 
-    def printMiddle(self): 
+    # Function to get the middle of the linked list
+    def printMiddle(self):
+        middle = self.length // 2
+        current = self.head
+        for _ in range(middle):
+            current = current.next
+
+        print(f"middle node value: {current.data} - index: {middle}")
 
 # Driver code 
 list1 = LinkedList() 

Exercise_4.py

@@ -1,12 +1,31 @@
 # Python program for implementation of MergeSort 
 def mergeSort(arr):
-
-  #write your code here
+  if len(arr) <= 1:
+    return
+
+  mid = len(arr) // 2
+  left = arr[:mid]
+  right = arr[mid:]
+
+  mergeSort(left)
+  mergeSort(right)
+
+  leftIndex = rightIndex = combinedIndex = 0
+  while leftIndex < len(left) and rightIndex < len(right):
+    if left[leftIndex] <= right[rightIndex]:
+      arr[combinedIndex] = left[leftIndex]
+      leftIndex += 1
+    else:
+      arr[combinedIndex] = right[rightIndex]
+      rightIndex += 1
+
+    combinedIndex += 1
+
+    arr[combinedIndex:] = left[leftIndex:] + right[rightIndex:]
 
 # Code to print the list 
 def printList(arr): 
-
-    #write your code here
+  print(*arr)    
 
 # driver code to test the above code 
 if __name__ == '__main__':