Update EX 1B Merge sort.md

EX 1B Merge sort.md

@@ -1,27 +1,103 @@
 # EX 1B Merge Sort
-## DATE:
+## DATE:22.02.2025
 ## AIM:
 To write a python program to sort the first half of the list using merge sort.
 
 ## Algorithm
-1. 
-2. 
-3. 
-4.  
-5.   
+1.  Initialize an empty list arr
+2. Read an integer n (number of elements) from the user
+3. Repeat n times:
+   Read each integer and append it to the list arr
+4.Display the original array
+5.Define a function merge(arr, l, m, r) to merge two sorted halves:
+  • Create two temporary arrays L and R for the left and right subarrays
+  • Copy data into temporary arrays
+  • Merge the two temporary arrays back into arr[l..r]
+  • Copy any remaining elements of L[] and R[], if any
+6.Define a recursive function mergeSort(arr, l, r) to sort an array segment:
+  • If l < r:
+    – Find middle point m
+    – Recursively call mergeSort(arr, l, m)
+    – Recursively call mergeSort(arr, m+1, r)
+    – Call merge(arr, l, m, r) to merge sorted parts
+7.Sort only the first half of the list:
+  • Call mergeSort(arr, 0, (n//2) - 1)
+
+8.Display the modified array
 
 ## Program:
 ```
-/*
+
 Program to implement Merge Sort
-Developed by: 
-Register Number:  
-*/
+Developed by: M.PAVITHRA
+Register Number: 212222100032
+
+def merge(arr, l, m, r):
+    n1 = m - l + 1
+    n2 = r - m
+    L = [0] * (n1)
+    R = [0] * (n2)
+    for i in range(0, n1):
+        L[i] = arr[l + i]
+
+    for j in range(0, n2):
+        R[j] = arr[m + 1 + j]
+
+
+    i = 0     
+    j = 0     
+    k = l     
+
+    while i < n1 and j < n2:
+        if L[i] <= R[j]:
+            arr[k] = L[i]
+            i += 1
+        else:
+            arr[k] = R[j]
+            j += 1
+        k += 1
+
+    # Copy the remaining elements of L[], if there
+    # are any
+    while i < n1:
+        arr[k] = L[i]
+        i += 1
+        k += 1
+
+    while j < n2:
+        arr[k] = R[j]
+        j += 1
+        k += 1
+
+def mergeSort(arr, l, r):
+    if l < r:
+        m = l+(r-l)//2
+        mergeSort(arr, m+1, r)
+        merge(arr, l, m, r)
+
+
+
+arr =[]               #[12, 11, 13, 5, 6, 7]
+n =int(input())
+for i in range(n):
+    arr.append(int(input()))
+print("Given array is")
+for i in range(n):
+    print("%d" % arr[i],end=" ")
+
+mergeSort(arr, 0, n-1)
+print("\n\nSorted array is")
+for i in range(n):
+    print("%d" % arr[i],end=" ")
+
+
 ```
 
 ## Output:
 
+![Screenshot 2025-04-29 105434](https://github.com/user-attachments/assets/acec68d8-eb0f-4efd-83a7-ef3cc24a73e4)
 
 
 ## Result:
+
 The program successfully sorts the first half of the given array using merge sort. where only the first half is sorted, and the second half remains unchanged.