Basic Algorithms

def selectionSort (a):
  for i in range (len(a) - 1):
    # find the minimum
    min = a[i]
    minIdx = i

    for j in range (i + 1, len(a)):
      if (a[j] < min):
        min = a[j]
	minIdx = j

    # Swap the minimum element with the element at the ith place
    a[minIdx] = a[i]
    a[i] = min

def sequentialSearch (a, x):
  for i in range (len(a)):
    if (a[i] == x):
      return i
  return -1

def binarySearch (a, x):
  lo = 0
  hi = len(a) - 1
  while (lo <= hi):
    mid = (lo + hi) // 2
    if (x > a[mid]):
      lo = mid + 1
    elif (x < a[mid]):
      hi = mid - 1
    else:
      return mid
  return -1

def merge (a, b):
  c = []
  idxA = 0
  idxB = 0

  while ((idxA < len(a)) and (idxB < len(b))):
    if (a[idxA] < b[idxB]):
      c.append (a[idxA])
      idxA = idxA + 1
    else:
      c.append (b[idxB])
      idxB = idxB + 1

  # if a is not empty write it out 
  while (idxA < len(a)):
    c.append (a[idxA])
    idxA = idxA + 1

  # if b is not empty write it out
  while (idxB < len(b)):
    c.append (b[idxB])
    idxB = idxB + 1

  return c

def main():
  print ("Test selection sort")
  a = [9, 1, 8, 2, 7, 3, 6, 4, 5]
  print (a)
  selectionSort (a)
  print (a)
  print ()


  print ("Test sequential search")
  x = 3
  print (str(x) + " " + str(sequentialSearch (a, x)))
  x = 25
  print (str(x) + " " + str(sequentialSearch (a, x)))
  print ()

  print ("Test binary search")
  x = 3
  print (str(x) + " " + str(binarySearch (a, x)))
  x = 25
  print (str(x) + " " + str(binarySearch (a, x)))
  print ()

  print ("Test merge")
  a = [1, 3, 5, 7, 9]
  b = [2, 4, 6, 8]
  c = merge (a, b)
  print (a)
  print (b)
  print (c)
  print ()

main()