Added quicksort with 3 way partition in python

Algorithms/sorting/quickSort_3partition.py

@@ -0,0 +1,36 @@
+# Uses python3
+import sys
+import random
+
+def partition3(a, l, r):
+    x=a[l]
+    m1=l
+    m2=l
+    for i in range(l + 1, r + 1):
+        if a[i] < x:
+            a[i], a[m1] = a[m1], a[i]
+            a[i], a[m2+1] = a[m2+1], a[i]
+            m1 += 1
+            m2 += 1
+        elif a[i] == x:
+            a[i], a[m2+1] = a[m2+1], a[i]
+            m2 += 1
+    return (m1,m2)
+
+def randomized_quick_sort(a, l, r):
+    if l >= r:
+        return
+    k = random.randint(l, r)
+    a[l], a[k] = a[k], a[l]
+    #use partition3
+    m1,m2 = partition3(a, l, r)
+    randomized_quick_sort(a, l, m1 - 1);
+    randomized_quick_sort(a, m2 + 1, r);
+
+
+n=int(input())
+lst=list(map(int,input().split()))
+randomized_quick_sort(lst,0,n-1)
+lst=list(map(str,lst))
+st=" "
+print(st.join(lst))