Completed precourse 2 (couldnt do the iterative run for the quicksort)

Exercise_1.py

@@ -3,20 +3,35 @@
 
 # It returns location of x in given array arr  
 # if present, else returns -1 
+
+#TC of binary search is O(log n) since we halve the work to be done at each division
+#SC is also o(log n) as we only use the part that potentially has the element
 def binarySearch(arr, l, r, x): 
 
   #write your code here
-
-
+  n = len(arr)
+  l = 0
+  r = n - 1
+
+  while l <= r:
+     m = (l + r) // 2
+     if arr[m] == x:
+        return m
+     elif arr[m] <x:
+        l = m + 1
+     else:
+        r = m - 1
+  return -1
+
 
 # Test array 
 arr = [ 2, 3, 4, 10, 40 ] 
-x = 10
+x = 1
 
 # Function call 
 result = binarySearch(arr, 0, len(arr)-1, x) 
 
 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

@@ -1,15 +1,31 @@
 # Python program for implementation of Quicksort Sort 
+#TC is O(n^2) in the worst case (wrong pivot selection) and o(n log n) in the average of best case
+#SC is o(n)
 
 # give you explanation for the approach
 def partition(arr,low,high):
+    p = arr[low]
+    i = low + 1
+    j = high
+    while True:
+        while i <= j and arr[i] <= p: #shifts all the elements less than pivot to left
+            i += 1
+        while i <= j and arr[j] >= p: #shifts all the elements greater than pivot to right
+            j -= 1
+        if i <= j:
+            arr[i], arr[j] = arr[j], arr[i] #shifting done here
+        else:
+            break
+    arr[low], arr[j] = arr[j], arr[low] #swaping of pivot and the jth element, point where pivot is correctly placed
+    return j
 
-
-    #write your code here
-
-
 # Function to do Quick sort 
 def quickSort(arr,low,high): 
-
+    if low < high:
+        pivot = partition(arr, low, high) #calls for the position of pivot
+        quickSort(arr, low, pivot - 1) #recusrive call ofor left
+        quickSort(arr, pivot + 1, high) #recusrive call on right
+
     #write your code here
 
 # Driver code to test above 

Exercise_3.py

@@ -1,20 +1,33 @@
 # Node class  
+#TC is o(n) since the fast pointer moves thorugh all the elements
+#SC is o(N) for pushing, and maybe constant for the finding part, since we use only two pointers
 class Node:  
 
     # Function to initialise the node object  
     def __init__(self, data):  
+        self.data = data
+        self.next = None
 
 class LinkedList: 
 
     def __init__(self): 
+        self.head = None
 
 
     def push(self, new_data): 
-
+        newNode = Node(new_data)
+        newNode.next = self.head #push the earlier head as the next element of the new node to be added
+        self.head = newNode #eastablish the new node as head
 
     # Function to get the middle of  
     # the linked list 
     def printMiddle(self): 
+        slow, fast = self.head, self.head #slow and fast pointer, bcz fast jumps twice as compared to slow, when the fast will be at the end, the slow will be in the mid
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+        return slow
+
 
 # Driver code 
 list1 = LinkedList() 
@@ -23,4 +36,4 @@ def printMiddle(self):
 list1.push(2) 
 list1.push(3) 
 list1.push(1) 
-list1.printMiddle() 
+print("Middle element:", list1.printMiddle().data) 

Exercise_4.py

@@ -1,10 +1,46 @@
 # Python program for implementation of MergeSort 
+
+#TC for mergesort in any condition is O(nlogn)
+#SC is o(n)
 def mergeSort(arr):
+    if len(arr) <= 1:
+        return arr
+
+    mid = (len(arr)) //2
+    left = arr[:mid]
+    right = arr[mid:]
+    lhalf = mergeSort(left)
+    rhalf = mergeSort(right)
+    return merge(lhalf, rhalf)
+
+def merge(left, right):
+    res =[]
+    i, j = 0, 0
+    while i < len(left) and j < len(right):
+        if left[i] < right[j]:
+
+          res.append(left[i])
+          i += 1
+        else:  
+          res.append(right[j])
+          j += 1
+    res.extend(left[i:])
+    res.extend(right[j:])
+    return res
+
+
+
 
   #write your code here
 
 # Code to print the list 
 def printList(arr): 
+   for i in arr:
+      print(i, end =" ")
+   print()
+
+
+
 
     #write your code here
 
@@ -13,6 +49,6 @@ def printList(arr):
     arr = [12, 11, 13, 5, 6, 7]  
     print ("Given array is", end="\n")  
     printList(arr) 
-    mergeSort(arr) 
+    arr = mergeSort(arr) 
     print("Sorted array is: ", end="\n") 
     printList(arr) 

Exercise_5.py

@@ -2,9 +2,22 @@
 
 # This function is same in both iterative and recursive
 def partition(arr, l, h):
+    p = arr[low]
+    i = low + 1
+    j = high
+    while True:
+        while i <= j and arr[i] <= p: #shifts all the elements less than pivot to left
+            i += 1
+        while i <= j and arr[j] >= p: #shifts all the elements greater than pivot to right
+            j -= 1
+        if i <= j:
+            arr[i], arr[j] = arr[j], arr[i] #shifting done here
+        else:
+            break
+    arr[low], arr[j] = arr[j], arr[low] #swaping of pivot and the jth element, point where pivot is correctly placed
+    return j
   #write your code here
 
 
 def quickSortIterative(arr, l, h):
-  #write your code here
-
+  #write your code he