2019-03-05 in class

histogram.py

@@ -1,30 +1,27 @@
 #!/usr/bin/env python3
+# vim: set sw=4 ts=4 et tw=80:
 
 import sys
 
 def histogram(data):
-    height_max = max(data)
-    height_min = min(min(data), 0)
-    current_line = height_max
+    top = max(max(data), 0)
+    bottom = min(min(data), 0)
+    i = top
 
-    while current_line >= height_min:
+    while i >= bottom:
         to_print = ""
 
-        if current_line == 0:
-            print("-" * len(data))
-        else:
         for elem in data:
-                if current_line > 0 and elem >= current_line:
-                    to_print += "#"
-                elif current_line > 0:
-                    to_print += " "
-                elif current_line < 0 and elem <= current_line:
+            if i == 0:
+                to_print += "-"
+            elif (i > 0 and elem >= i) or \
+                 (i < 0 and elem <= i):
                 to_print += "#"
             else:
                 to_print += " "
         print(to_print)
 
-        current_line = current_line - 1
+        i = i - 1
 
 def main():
     args = [int(x) for x in sys.argv[1:]]

insertion_sort.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
+# vim: set ts=4 sw=4 et tw=80:
 
 import sys
 
@@ -10,9 +11,8 @@ def insertionsort(A):
         print(A)
         print(A)
         i = j - 1
-        tomove = A[j]
-        while i >= 0 and tomove < A[i]:
-            if A[i] > A[i+1]:
+        # while swapping is necessary or at the end of array
+        while i >= 0 and A[i+1] < A[i]:
             # Swap A[i] and A[j]
             A[i+1], A[i] = A[i], A[i+1]
             i = i - 1

mergesort.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+# vim: set ts=4 sw=4 et tw=80:
+
+import sys
+import math
+
+def find(A,x):
+    for a in A:
+        if a == x:
+            return True
+    return False
+
+def merge(A,B):
+    X = []
+    for a in A:
+        if not find(X, a):
+            X.append(a)
+    for b in B:
+        if not find(X, b):
+            X.append(b)
+    return X
+
+def mergesort(A):
+    l = len(A)
+    if l < 2:
+        return A
+    else:
+        lh = len(A) // 2
+        h1 = mergesort(A[:lh])
+        h2 = mergesort(A[lh:])
+        return merge(h1,h2)
+
+args = [int(x) for x in sys.argv[1:]]
+print(mergesort(args))

notes.md

@@ -94,3 +94,8 @@ Proof sort of by induction.
 
 An algorithm is correct if given an input the output satisfies the conditions
 stated. The algorithm must terminate.
+
+### The loop invariant
+
+Invariant condition able to make a loop equivalent to a straight path in an
+execution graph.