Added Insertion and Selection sort to the python folders. (#22)

* Added Insertion and Selection sort to the python folders.

* Loop(s) bound issues resolved; semantics of pseudocode to the range function recognized.

Co-authored-by: Christopher Lee <christopherlee@wireless-10-104-179-111.umd.edu>

sorting/README.md

@@ -14,6 +14,8 @@
 ### Python
 
 1. [Bubble Sort](python/bubble-sort.py)
+2. [Insertion Sort](python/insertion-sort.py)
+2. [Selection Sort](python/selection-sort.py)
 
 ### JavaScript
 

sorting/python/insertion-sort.py

@@ -0,0 +1,30 @@
+"""
+Analogizing this algorithm with inserting a playing 
+card into your hand, we distinguish the "key" as
+the inserting card and find the position of that 
+card among the previous j - 1 cards. 
+
+O(n^2) runtime (the deck is sorted in descending order).
+"""
+
+def insertionSort(A):
+	N = len(A)
+
+	for j in range(1, N):
+		key = A[j]
+		#insert the key into the sorted sequence A[1, ... , j - 1]
+		i = j - 1
+		while i >= 0 and A[i] > key:
+			A[i + 1] = A[i]
+			i -= 1
+
+		A[i + 1] = key
+
+
+A = [12, 3, 7, 22, -12, 100, 1]
+insertionSort(A)
+
+print("Sorted array: ")
+for ele in A:
+	print("\t" + str(ele))
+

sorting/python/selection-sort.py

@@ -0,0 +1,37 @@
+'''
+Find the largest element and place that element at the bottom
+of the list. Repeat for each sub-array. 
+
+O(n^2) time complexity. 
+'''
+def selectionSort(A):
+	N = len(A)
+
+	for i in range(N - 1, 0, -1):
+		k = 0
+
+		for j in range(1, i + 1):
+			if A[j] > A[k]:
+				k = j
+		swap(A, k, i)
+
+
+def swap(A, k, i):
+	"""
+	Helper function for swapping elements of the array. 
+	"""
+	tmp = A[k] 
+	A[k] = A[i]
+	A[i] = tmp
+
+
+# A = [12, 3, 7, 22, -12, 100, 1]
+# A = [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
+# A = [4, 1, 3, 9, 7]
+A = [5, 4, 3, 2, 1]
+
+selectionSort(A)
+
+print("Sorted array: ")
+for ele in A:
+	print("\t" + str(ele))