From: David Kerkeslager <kerkeslager@gmail.com>
Date: Fri, 13 Sep 2019 06:56:05 +0000 (-0400)
Subject: In-place mergesort
X-Git-Url: https://code.kerkeslager.com/?a=commitdiff_plain;h=e2a4297a839c1f0e36aba7afacd3bd308111c30f;p=sandbox

In-place mergesort
---

diff --git a/sort.py b/sort.py
new file mode 100644
index 0000000..72ef375
--- /dev/null
+++ b/sort.py
@@ -0,0 +1,104 @@
+def swap(xs, a, b):
+    swap.counter += 1
+    temp = xs[a]
+    xs[a] = xs[b]
+    xs[b] = temp
+
+swap.counter = 1
+
+def merge(xs, start, divide, end):
+    if divide < end:
+        while start < divide and xs[start] < xs[divide]:
+            start += 1
+
+        if start == divide:
+            return
+
+    else:
+        return
+
+    # if start < divide is implied by the most recent check
+    while divide < end and xs[divide - 1] < xs[end - 1]:
+        end -= 1
+
+    if divide == end:
+        return
+
+    swap(xs, start, divide)
+    start += 1
+
+    i = start
+    j = divide + 1
+
+    while i < divide and j < end:
+        if xs[i] < xs[j]:
+            i += 1
+        else:
+            swap(xs, i, j)
+            i += 1
+            j += 1
+
+    # 100K
+    #merge(xs, start, i, divide)
+    #merge(xs, divide, j, end)
+    #merge(xs, start, divide, end)
+
+    # 100K
+    #merge(xs, start, i, divide)
+    #merge(xs, start, divide, j)
+    #merge(xs, start, j, end)
+
+    # 80K
+    #merge(xs, i, divide, j)
+    #merge(xs, start, i, j)
+    #merge(xs, start, j, end)
+
+    # 80K
+    #merge(xs, i, divide, j)
+    #merge(xs, i, j, end)
+    #merge(xs, start, i, end)
+
+    # 80K
+    merge(xs, divide, j, end)
+    merge(xs, i, divide, end)
+    merge(xs, start, i, end)
+
+def sort(xs):
+    divisions = [0]
+
+    for i in range(len(xs) - 1):
+        if xs[i] > xs[i + 1]:
+            divisions.append(i + 1)
+
+    divisions.append(len(xs))
+
+    while len(divisions) > 2:
+        new_divisions = divisions[:]
+
+        for i in range(1,len(divisions) - 1,2):
+            merge(xs, divisions[i - 1], divisions[i], divisions[i + 1])
+            new_divisions.remove(divisions[i])
+
+        divisions = new_divisions
+
+xs = [i for i in range(1000)]
+import random
+random.shuffle(xs)
+
+print(xs)
+
+sort(xs)
+
+print(xs)
+
+print('Swaps:', swap.counter)
+
+def group_swap(xs, start, divide, end):
+    if start == divide or divide == end:
+        return
+
+    width = divide - start
+    for i in range(start, end):
+        swap(xs, i, i + width if i + width < end else start + i + width - end)
+
+print(xs)