Create merge_sort.py

Divide and Conquer/merge_sort.py

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+
+#thus function merges the subarrays
+def merge(arr, left ,mid ,right) :
+    n1 = int(mid - left + 1)
+    n2 = int(right - mid)
+
+    #Creating temporary left and
+    #right subarrays
+    L = [0] * (n1)
+    R = [0] * (n2)
+
+    #Filling the subarrays
+    for i in range(0,n1):
+        L[i] = arr[left + i]
+
+    for j in range(0,n2):
+        R[j] = arr[mid + j + 1]
+
+    i = 0
+    j = 0
+    k = left;
+
+    #Merge operation
+    while i < n1 and j < n2 :
+        if L[i] <= R[j]:
+            arr[k] = L[i]
+            k+=1
+            i+=1
+        else:
+            arr[k] = R[j]
+            k+=1
+            j+=1
+
+    #Remaining elements of left subarray      
+    while i < n1:
+        arr[k] = L[i]
+        k+=1
+        i+=1
+
+
+    #Remaining elements of right subarray
+    while j < n2:
+        arr[k] = R[j]
+        k+=1
+        j+=1
+
+
+#mergesort function       
+def mergeSort(arr, left, right):
+
+    if left < right:
+        #calculating mid
+        mid = int((left + (right - 1)) / 2)
+
+        #sort left subarray
+        mergeSort(arr, left, mid)
+        #sort right subarray
+        mergeSort(arr, mid + 1, right)
+        #merge left and right subarray
+        merge(arr, left, mid, right)
+
+
+#sample array to be sorted
+arr = [4, 5, 1, 2, -2, 0]
+size = len(arr)
+print("Before sorting : ")
+
+for i in range(size):
+    print("%d" %arr[i]);
+
+mergeSort(arr, 0, size - 1);
+
+print("After sorting : ")
+
+for j in range(size):
+    print("%d" %arr[j]);
+
+