adding pre-course2 solutions

Exercise_1.py

@@ -1,22 +1,29 @@
-# Python code to implement iterative Binary  
-# Search. 
-
-# It returns location of x in given array arr  
-# if present, else returns -1 
-def binarySearch(arr, l, r, x): 
-
-  #write your code here
-
-
-
-# Test array 
-arr = [ 2, 3, 4, 10, 40 ] 
+# Python code to implement iterative Binary Search.
+
+# It returns location of x in given array arr
+# if present, else returns -1
+def binarySearch(arr, l, r, x):
+    while l <= r:
+        mid = l + (r - l) // 2
+
+        if arr[mid] == x:
+            return mid
+        elif arr[mid] < x:
+            l = mid + 1
+        else:
+            r = mid - 1
+
+    return -1
+
+
+# Test array
+arr = [2, 3, 4, 10, 40]
 x = 10
-  
-# Function call 
-result = binarySearch(arr, 0, len(arr)-1, x) 
-  
-if result != -1: 
-    print "Element is present at index % d" % result 
-else: 
-    print "Element is not present in array"
+
+# Function call
+result = binarySearch(arr, 0, len(arr) - 1, x)
+
+if result != -1:
+    print("Element is present at index %d" % result)
+else:
+    print("Element is not present in array")

Exercise_2.py

@@ -1,23 +1,38 @@
-# Python program for implementation of Quicksort Sort 
-
-# give you explanation for the approach
-def partition(arr,low,high):
-
-
-    #write your code here
-
-
-# Function to do Quick sort 
-def quickSort(arr,low,high): 
-
-    #write your code here
-
-# Driver code to test above 
-arr = [10, 7, 8, 9, 1, 5] 
-n = len(arr) 
-quickSort(arr,0,n-1) 
-print ("Sorted array is:") 
-for i in range(n): 
-    print ("%d" %arr[i]), 
-
-
+# Python program for implementation of Quick Sort
+
+# Approach:
+# Pick the last element as pivot.
+# Place all smaller elements before pivot and greater elements after pivot.
+# Then recursively sort the left and right parts.
+
+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):
+    if low < high:
+        pi = partition(arr, low, high)
+
+        quickSort(arr, low, pi - 1)
+        quickSort(arr, pi + 1, high)
+
+
+# Driver code to test above
+arr = [10, 7, 8, 9, 1, 5]
+n = len(arr)
+
+quickSort(arr, 0, n - 1)
+
+print("Sorted array is:")
+for i in range(n):
+    print("%d" % arr[i], end=" ")

Exercise_3.py

@@ -1,26 +1,42 @@
-# Node class  
-class Node:  
-
-    # Function to initialise the node object  
-    def __init__(self, data):  
-
-class LinkedList: 
-
-    def __init__(self): 
-
-
-    def push(self, new_data): 
-
-
-    # Function to get the middle of  
-    # the linked list 
-    def printMiddle(self): 
-
-# Driver code 
-list1 = LinkedList() 
-list1.push(5) 
-list1.push(4) 
-list1.push(2) 
-list1.push(3) 
-list1.push(1) 
-list1.printMiddle() 
+# Node class
+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):
+        new_node = Node(new_data)
+        new_node.next = self.head
+        self.head = new_node
+
+    # Function to get the middle of
+    # the linked list
+    def printMiddle(self):
+        slow_ptr = self.head
+        fast_ptr = self.head
+
+        if self.head is not None:
+            while fast_ptr is not None and fast_ptr.next is not None:
+                fast_ptr = fast_ptr.next.next
+                slow_ptr = slow_ptr.next
+
+            print("The middle element is:", slow_ptr.data)
+
+
+# Driver code
+list1 = LinkedList()
+list1.push(5)
+list1.push(4)
+list1.push(2)
+list1.push(3)
+list1.push(1)
+
+list1.printMiddle()

Exercise_4.py

@@ -1,18 +1,52 @@
-# Python program for implementation of MergeSort 
+# Python program for implementation of MergeSort
+
 def mergeSort(arr):
-
-  #write your code here
-
-# Code to print the list 
-def printList(arr): 
-
-    #write your code here
-
-# driver code to test the above code 
-if __name__ == '__main__': 
-    arr = [12, 11, 13, 5, 6, 7]  
-    print ("Given array is", end="\n")  
-    printList(arr) 
-    mergeSort(arr) 
-    print("Sorted array is: ", end="\n") 
-    printList(arr) 
+    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):
+    for i in range(len(arr)):
+        print(arr[i], end=" ")
+    print()
+
+
+# driver code to test the above code
+if __name__ == '__main__':
+    arr = [12, 11, 13, 5, 6, 7]
+
+    print("Given array is", end="\n")
+    printList(arr)
+
+    mergeSort(arr)
+
+    print("Sorted array is: ", end="\n")
+    printList(arr)

Exercise_5.py

@@ -1,10 +1,61 @@
-# Python program for implementation of Quicksort
+# Python program for implementation of Iterative Quicksort
 
 # 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
+    size = h - l + 1
+    stack = [0] * size
+
+    top = -1
+
+    top += 1
+    stack[top] = l
+
+    top += 1
+    stack[top] = h
+
+    while top >= 0:
+        h = stack[top]
+        top -= 1
+
+        l = stack[top]
+        top -= 1
+
+        p = partition(arr, l, h)
+
+        if p - 1 > l:
+            top += 1
+            stack[top] = l
+
+            top += 1
+            stack[top] = p - 1
+
+        if p + 1 < h:
+            top += 1
+            stack[top] = p + 1
+
+            top += 1
+            stack[top] = h
+
+
+# Driver code to test above
+arr = [10, 7, 8, 9, 1, 5]
+n = len(arr)
+
+quickSortIterative(arr, 0, n - 1)
 
+print("Sorted array is:")
+for i in range(n):
+    print("%d" % arr[i], end=" ")