From 0b2b2d7a92f0f0e7ae8f25ffe410831ca47dd99d Mon Sep 17 00:00:00 2001
From: prenastro <prenastro@gmail.com>
Date: Sun, 28 Jun 2026 02:57:08 -0700
Subject: [PATCH 1/2] Completed S30 pre-course2

---
 Exercise_1.py | 26 +++++++++++++++++++-------
 Exercise_2.py | 28 ++++++++++++++++++++++++----
 Exercise_3.py | 32 ++++++++++++++++++++++++++++----
 Exercise_4.py | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
 Exercise_5.py | 34 ++++++++++++++++++++++++++++++++--
 test.py       |  6 ++++++
 6 files changed, 155 insertions(+), 19 deletions(-)
 create mode 100644 test.py

diff --git a/Exercise_1.py b/Exercise_1.py
index 3e6adcf4..7823a4a8 100644
--- a/Exercise_1.py
+++ b/Exercise_1.py
@@ -4,11 +4,19 @@
 # It returns location of x in given array arr  
 # if present, else returns -1 
 def binarySearch(arr, l, r, x): 
-  
-  #write your code here
-  
-    
-  
+
+      #write your code here
+
+      while l<=r:
+          m = (l + r)// 2
+          if arr[m]>x:
+              r = m-1
+          elif arr[m]<x:
+              l = m+1
+          else:
+              return m
+      return -1
+
 # Test array 
 arr = [ 2, 3, 4, 10, 40 ] 
 x = 10
@@ -17,6 +25,10 @@ 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 % d" % result)
 else: 
-    print "Element is not present in array"
+    print("Element is not present in array")
+
+
+# TC - O(logn)
+# SC - O(1)
\ No newline at end of file
diff --git a/Exercise_2.py b/Exercise_2.py
index 35abf0dd..c71434ef 100644
--- a/Exercise_2.py
+++ b/Exercise_2.py
@@ -2,15 +2,33 @@
   
 # give you explanation for the approach
 def partition(arr,low,high):
-  
-  
     #write your code here
-  
+    pivot = arr[high]      # choose last element as pivot
+    i = low - 1            # index of smaller element
+
+    for j in range(low, high):
+        if arr[j] <= pivot:
+            i += 1
+            arr[i], arr[j] = arr[j], arr[i]
+
+    # place pivot in correct position
+    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
+    if low < high:
+        pi = partition(arr, low, high)
+
+        # sort left part
+        quickSort(arr, low, pi - 1)
+
+        # sort right part
+        quickSort(arr, pi + 1, high)
   
 # Driver code to test above 
 arr = [10, 7, 8, 9, 1, 5] 
@@ -18,6 +36,8 @@ def quickSort(arr,low,high):
 quickSort(arr,0,n-1) 
 print ("Sorted array is:") 
 for i in range(n): 
-    print ("%d" %arr[i]), 
+    print ("%d" %arr[i])
   
  
+# TC O(nlogn)
+# SC O(logn) - average O(n)- worst case
\ No newline at end of file
diff --git a/Exercise_3.py b/Exercise_3.py
index a26a69b8..f088d03d 100644
--- a/Exercise_3.py
+++ b/Exercise_3.py
@@ -2,19 +2,39 @@
 class Node:  
   
     # Function to initialise the node object  
-    def __init__(self, data):  
+    def __init__(self, data):
+        self.data = data
+        self.next = None
         
 class LinkedList: 
   
-    def __init__(self): 
+    def __init__(self):
+        self.head = None
+        self.tail = None
         
   
-    def push(self, new_data): 
+    def push(self, new_data):
+        new_node = Node(new_data)
+
+        if self.head is None:
+            self.head = self.tail = new_node
+        else:
+            self.tail.next = new_node
+            self.tail = new_node
         
   
     # Function to get the middle of  
     # the linked list 
-    def printMiddle(self): 
+    def printMiddle(self):
+        slow = fast = self.head
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+            #print(slow.data)
+            #print(fast.data)
+
+        print(slow.data)
+
 
 # Driver code 
 list1 = LinkedList() 
@@ -24,3 +44,7 @@ def printMiddle(self):
 list1.push(3) 
 list1.push(1) 
 list1.printMiddle() 
+
+
+# TC O(n)
+# SC O(1)
\ No newline at end of file
diff --git a/Exercise_4.py b/Exercise_4.py
index 9bc25d3d..4862cb0c 100644
--- a/Exercise_4.py
+++ b/Exercise_4.py
@@ -1,13 +1,54 @@
 # Python program for implementation of MergeSort 
 def mergeSort(arr):
+    # write your code here
+
+    if len(arr) > 1:
+        mid = len(arr) // 2
+
+        # Divide
+        left = arr[:mid]
+        right = arr[mid:]
+
+        # Recursively sort both halves
+        mergeSort(left)
+        mergeSort(right)
+
+        # Merge the two sorted halves
+        i = j = k = 0
+
+        # Compare elements from left and right
+        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
+
+        # Copy remaining elements of left
+        while i < len(left):
+            arr[k] = left[i]
+            i += 1
+            k += 1
+
+        # Copy remaining elements of right
+        while j < len(right):
+            arr[k] = right[j]
+            j += 1
+            k += 1
   
-  #write your code here
+
   
 # Code to print the list 
 def printList(arr): 
     
     #write your code here
-  
+        for x in arr:
+            print(x, end=" ")
+        print()
+
+
 # driver code to test the above code 
 if __name__ == '__main__': 
     arr = [12, 11, 13, 5, 6, 7]  
@@ -16,3 +57,6 @@ def printList(arr):
     mergeSort(arr) 
     print("Sorted array is: ", end="\n") 
     printList(arr) 
+
+# TC - O(nlogn)
+# SC - O(n)
\ No newline at end of file
diff --git a/Exercise_5.py b/Exercise_5.py
index 1da24ffb..7e900338 100644
--- a/Exercise_5.py
+++ b/Exercise_5.py
@@ -2,9 +2,39 @@
 
 # This function is same in both iterative and recursive
 def partition(arr, l, h):
-  #write your code here
+   #write your code here
+    pivot = arr[h]
+    i = l
+
+    for j in range(l, h):
+        if arr[j] <= pivot:
+            arr[i], arr[j] = arr[j], arr[i]
+            i += 1
+
+    arr[i], arr[h] = arr[h], arr[i]
+    return i
 
 
 def quickSortIterative(arr, l, h):
-  #write your code here
+    # write your code here
+    stack = [(l, h)]
+
+    while stack:
+        l, h = stack.pop()
+
+        if l >= h:
+            continue
+
+        p = partition(arr, l, h)
+
+        stack.append((l, p - 1))
+        stack.append((p + 1, h))
+
+
+# Driver code (NO INDENTATION)
+arr = [10, 7, 8, 9, 1, 5]
+quickSortIterative(arr, 0, len(arr) - 1)
+print(arr)
 
+# TC - O(nlogn)
+# SC - O(logn) - average O(n^2) worst case
\ No newline at end of file
diff --git a/test.py b/test.py
new file mode 100644
index 00000000..cfd73b66
--- /dev/null
+++ b/test.py
@@ -0,0 +1,6 @@
+def getMinimumTime(requestedHubs, transitionTime):
+    m = len(requestedHubs)
+
+    pre = [0] * (m+1)
+    for i in range(1, m+1):
+        pre[i] = pre[i-1] + requestedHubs[i]

From ea29689796bd2de0a77bac0c8a2be4b1bbecab43 Mon Sep 17 00:00:00 2001
From: Preranathm <prenastro@users.noreply.github.com>
Date: Sun, 28 Jun 2026 02:59:57 -0700
Subject: [PATCH 2/2] Delete unused file

---
 test.py | 6 ------
 1 file changed, 6 deletions(-)
 delete mode 100644 test.py

diff --git a/test.py b/test.py
deleted file mode 100644
index cfd73b66..00000000
--- a/test.py
+++ /dev/null
@@ -1,6 +0,0 @@
-def getMinimumTime(requestedHubs, transitionTime):
-    m = len(requestedHubs)
-
-    pre = [0] * (m+1)
-    for i in range(1, m+1):
-        pre[i] = pre[i-1] + requestedHubs[i]