From 058769a0e2672768eb7f6bfd51e6353d9a63b2a6 Mon Sep 17 00:00:00 2001
From: jpg-130 <jigsgandhi97@gmail.com>
Date: Tue, 8 Oct 2019 18:32:34 +0530
Subject: [PATCH 1/2] mergesort added

---
 divide_and_conquer/mergesort.py | 39 +++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 divide_and_conquer/mergesort.py

diff --git a/divide_and_conquer/mergesort.py b/divide_and_conquer/mergesort.py
new file mode 100644
index 000000000000..f995ff397d34
--- /dev/null
+++ b/divide_and_conquer/mergesort.py
@@ -0,0 +1,39 @@
+def merge(a,b,m,e):
+    l=a[b:m+1]
+    r=a[m+1:e+1]
+    k=b
+    i=0
+    j=0
+    while i<len(l) and j<len(r):
+        #change sign for ascending order
+        if l[i]>r[j]: 
+            a[k]=l[i]
+            i+=1
+        else:
+            a[k]=r[j]
+            j+=1
+        k+=1
+    while i<len(l):
+        a[k]=l[i]
+        i+=1
+        k+=1
+    while j<len(r):
+        a[k]=r[j]
+        j+=1
+        k+=1
+    return a
+    
+def mergesort(a,b,e):
+    if b<e:
+        m = (b+e)//2
+        #print("ms1",a,b,m)
+        mergesort(a,b,m)
+        #print("ms2",a,m+1,e)
+        mergesort(a,m+1,e)
+        #print("m",a,b,m,e)
+        merge(a,b,m,e)
+        return a
+
+
+a=[3,2,1,0,1,2,3,5,4]
+print("Descending order",mergesort(a,0,len(a)-1))

From ec41c7cc720312bd04143a8ba924977ff4a9c67d Mon Sep 17 00:00:00 2001
From: jpg-130 <jigsgandhi97@gmail.com>
Date: Wed, 9 Oct 2019 10:28:28 +0530
Subject: [PATCH 2/2] added doctest

---
 divide_and_conquer/mergesort.py | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/divide_and_conquer/mergesort.py b/divide_and_conquer/mergesort.py
index f995ff397d34..b2a5a4c321ae 100644
--- a/divide_and_conquer/mergesort.py
+++ b/divide_and_conquer/mergesort.py
@@ -5,8 +5,8 @@ def merge(a,b,m,e):
     i=0
     j=0
     while i<len(l) and j<len(r):
-        #change sign for ascending order
-        if l[i]>r[j]: 
+        #change sign for Descending order
+        if l[i]<r[j]: 
             a[k]=l[i]
             i+=1
         else:
@@ -24,6 +24,12 @@ def merge(a,b,m,e):
     return a
     
 def mergesort(a,b,e):
+    """
+    >>> mergesort([3,2,1],0,2)
+    [1, 2, 3]
+    >>> mergesort([3,2,1,0,1,2,3,5,4],0,8)
+    [0, 1, 1, 2, 2, 3, 3, 4, 5]
+    """
     if b<e:
         m = (b+e)//2
         #print("ms1",a,b,m)
@@ -34,6 +40,6 @@ def mergesort(a,b,e):
         merge(a,b,m,e)
         return a
 
-
-a=[3,2,1,0,1,2,3,5,4]
-print("Descending order",mergesort(a,0,len(a)-1))
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()