Completed Precourse 2

Exercise_1.py

@@ -1,22 +1,31 @@
-# 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):
+
+    # write your code here
+    while l <= r:
+        m = l + (r - l) // 2
+        if arr[m] == x:
+            return m
+        elif arr[m] > x:
+            r = m - 1
+        else:
+            l = m + 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:", result)
+else:
+    print("Element is not present in array")

Exercise_2.py

@@ -1,23 +1,35 @@
-# Python program for implementation of Quicksort Sort 
-
+# 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):
+    # write your code here
+    pivot = arr[high]
+
+    start = low
+    for end in range(low, high):
+        if arr[end] <= pivot:
+            arr[start], arr[end] = arr[end], arr[start]
+            start+=1
+    arr[start], arr[high] = arr[high], arr[start]
+    return start
+
+
+# Function to do Quick sort
+def quickSort(arr, low, high):
+    # write your code here
+    if low < high:
+        index = partition(arr, low, high)
+        # Sort left half recursively
+        quickSort(arr, low, index - 1)
+        # Sort right half recursively
+        quickSort(arr, index + 1, high)
+
 
-# 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]), 
-
-
+# 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]),

Exercise_3.py

@@ -1,26 +1,38 @@
-# 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):
+        node = Node(new_data)
+        node.next = self.head
+        self.head = node
+
+    # Function to get the middle of
+    # the linked list
+    def printMiddle(self):
+        slow = self.head
+        fast = self.head
+        while fast != None and fast.next != None:
+            slow = slow.next
+            fast = fast.next.next
+        print(slow.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

@@ -1,10 +1,35 @@
 # Python program for implementation of MergeSort 
 def mergeSort(arr):
+    if len(arr)<=1:
+        return arr
+    mid=len(arr)//2
+    left = mergeSort(arr[:mid])
+    right = mergeSort(arr[mid:])
+
+    return merge(left,right)
 
   #write your code here
+def merge(left,right):
+    result=[]
+    i=0
+    j=0
+
+    while i<len(left) and j<len(right):
+        if left[i]<right[j]:
+            result.append(left[i])
+            i+=1
+        else:
+            result.append(right[j])
+            j+=1
+    result.extend(left[i:])
+    result.extend(right[j:])
+    return result
+
 
 # Code to print the list 
-def printList(arr): 
+def printList(arr):
+    for i in arr:
+        print(i,"\n") 
 
     #write your code here
 
@@ -13,6 +38,6 @@ 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

@@ -3,8 +3,35 @@
 # This function is same in both iterative and recursive
 def partition(arr, l, h):
   #write your code here
+  pivot=arr[h]
+  start=l
+  for end in range(l,h):
+    if arr[end]<=pivot:
+      arr[start],arr[end]=arr[end],arr[start]
+      start+=1
+  arr[start],arr[h]=arr[h],arr[start]
+  return start
 
 
 def quickSortIterative(arr, l, h):
   #write your code here
+  callstack=[]
+  callstack.append((l,h))
+  while callstack:
+    l,h=callstack.pop()
+    if l<h:
+      pivot = partition(arr,l,h)
+      if pivot-1>l:
+        callstack.append((l,pivot-1))
+      if pivot+1<h:
+        callstack.append((pivot+1,h))
+
+if __name__ == "__main__":
+    arr = [10, 7, 8, 9, 1, 5]
+    print("Before:", arr)
+
+    quickSortIterative(arr, 0, len(arr) - 1)
+
+    print("After: ", arr)
+