recursion continuation

Author: Blooverh

PythonDataStructsAndAlgo/Notes.md

@@ -18,4 +18,13 @@
 > Many common behaviors of an OS such as copying a directory or deleting a directory, are implemented using recursive algorithms.
 
 > ### Python OS module
-    > * *os module* 
+    > * *os module* -> provides robust tools for interacting with the operating system during execution of a program.
+>> os.path.getsize(path) - return imemediate disk usage (measure in bytes) for the file or directory that is identified by the string *path* (eg. /user/rt/courses). 
+
+>> os.path.isdir(path) - return True if entry designated by string path is a directory; False otherwise.
+
+>> os.listdir(path) -Return a list of strings that are names of all entries within a directory designated by string *path*
+
+>> os.path.join(path, filename) - Compose a path string name and filename string using an appropriate operating system separator between the two ("/" or "\\\"). Returning the string that represents the full path to the file.
+
+> Linear recursion - if a recursive function is designed so that each invocation of the body makes at most one new recursive call, this is known as linear recursion.

PythonDataStructsAndAlgo/Recursion/OsRecursion.py

@@ -0,0 +1,12 @@
+import os
+
+def disk_usage(path):
+    """Return the number of bytes used by a file or folder or any descendents."""
+    total= os.path.getsize(path) #account for direct usage
+    if os.path.isdir(path):
+        for filename in os.listdir(path, filename):
+            childpath= os.path.join(path, filename)
+            tota+= disk_usage(childpath)
+
+    print('{0:7}'.format(total), path)
+    return total

PythonDataStructsAndAlgo/Recursion/ReverseSeqRecursion.py

@@ -0,0 +1,11 @@
+# time complexity is O(n)
+def reverse(S, start, stop):
+    """Reverse elements in implicit slice S[start:stop]"""
+    if start < stop-1:
+        S[start] , S[stop-1] = S[stop-1], S[start]
+        reverse(S, start+1, stop-1)
+
+    return S
+
+list=[9,8,7,6,5,4,3,2,1,0]
+print(reverse(list, 0 , len(list)))

PythonDataStructsAndAlgo/Recursion/SumOfSequenceElements.py

@@ -0,0 +1,10 @@
+def linear_sum(S, n):
+    if n ==0:
+        return 0
+    else:
+        return linear_sum(S, n-1)+ S[n-1]
+    
+S=[4,3,6,2,8]
+n= len(S)
+
+print(linear_sum(S,n))

PythonDataStructsAndAlgo/Recursion/powerRecursion.py

@@ -0,0 +1,8 @@
+def power(x,n):
+    """Compute the value x**n for integer n without using power functio"""
+    if n==0:
+        return 1
+    else:
+        return x* power(x,n-1)
+    
+print(power(2,7))