Completed the Pre-course 2

Exercise_1.py

@@ -4,8 +4,15 @@
 # It returns location of x in given array arr  
 # if present, else returns -1 
 def binarySearch(arr, l, r, x): 
-
-  #write your code here
+  while l <= r:
+    m = l + (r - l)//2
+    if arr[m] == x:
+       return m
+    if x < arr[m]:
+       r = m - 1
+    else:
+       l = m + 1
+  return -1
 
 
 
@@ -17,6 +24,6 @@ def binarySearch(arr, l, r, x):
 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",result) 
 else: 
-    print "Element is not present in array"
+    print ("Element is not present in array")

Exercise_2.py

@@ -1,16 +1,30 @@
 # Python program for implementation of Quicksort Sort 
 
 # give you explanation for the approach
-def partition(arr,low,high):
-
-
-    #write your code here
-
+def partition(arr, low, high):
+    pivot = arr[high]
+    i = low - 1
+
+    for j in range(low, high):
+        if arr[j] <= pivot:
+            i += 1
+            arr[i], arr[j] = arr[j], arr[i]
+
+    arr[i + 1], arr[high] = arr[high], arr[i + 1]
+    return i + 1
 
 # Function to do Quick sort 
 def quickSort(arr,low,high): 
-
-    #write your code here
+  # base condition
+    if low >= high:
+        return
+
+    # partition the array
+    pi = partition(arr, low, high)
+
+    # recursively sort left and right parts
+    quickSort(arr, low, pi - 1)
+    quickSort(arr, pi + 1, high)
 
 # Driver code to test above 
 arr = [10, 7, 8, 9, 1, 5] 

Exercise_3.py

@@ -1,20 +1,31 @@
 # Node class  
-class Node:  
-
+class Node:
     # Function to initialise the node object  
-    def __init__(self, data):  
+    def __init__(self, data,next=None):
+        self.data = data
+        self.next = next
 
 class LinkedList: 
 
     def __init__(self): 
-
+        self.head = Node(-1)
 
-    def push(self, new_data): 
+    def push(self, new_data):
+        temp = self.head
+        while temp.next:
+            temp = temp.next
+        newNode = Node(new_data)
+        temp.next = newNode
 
 
     # Function to get the middle of  
     # the linked list 
-    def printMiddle(self): 
+    def printMiddle(self):
+        slow,fast = self.head.next,self.head.next
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+        print(slow.data)
 
 # Driver code 
 list1 = LinkedList() 

Exercise_4.py

@@ -1,12 +1,34 @@
 # Python program for implementation of MergeSort 
 def mergeSort(arr):
-
-  #write your code here
+  if len(arr) > 1:
+    mid = len(arr) // 2
+    left = arr[:mid]
+    right = arr[mid:]
+    mergeSort(left)
+    mergeSort(right)
+    i = j = k = 0
+    while i < len(left) and j < len(right):
+        if left[i] < right[j]:
+            arr[k] = left[i]
+            i += 1
+        else:
+            arr[k] = right[j]
+            j += 1
+        k += 1
+    while i < len(left):
+        arr[k] = left[i]
+        i += 1
+        k += 1
+    while j < len(right):
+        arr[k] = right[j]
+        j += 1
+        k += 1
 
 # Code to print the list 
-def printList(arr): 
-
-    #write your code here
+def printList(arr):
+  for item in arr:
+      print(item)
+
 
 # driver code to test the above code 
 if __name__ == '__main__': 

Exercise_5.py

@@ -2,9 +2,37 @@
 
 # This function is same in both iterative and recursive
 def partition(arr, l, h):
-  #write your code here
+    pivot = arr[h]
+    i = l - 1
+
+    for j in range(l, h):
+        if arr[j] <= pivot:
+            i += 1
+            arr[i], arr[j] = arr[j], arr[i]
+
+    arr[i + 1], arr[h] = arr[h], arr[i + 1]
+    return i + 1
 
 
 def quickSortIterative(arr, l, h):
-  #write your code here
+  # Create an explicit stack
+  stack = []
+
+  # push initial range
+  stack.append((l, h))
+
+  # Process stack until empty
+  while stack:
+      l, h = stack.pop()
+
+      # Partition the array
+      pi = partition(arr, l, h)
+
+      # If elements on left side of pivot, push left side
+      if pi - 1 > l:
+          stack.append((l, pi - 1))
+
+      # If elements on right side of pivot, push right side
+      if pi + 1 < h:
+          stack.append((pi + 1, h))