python Python.Data.Searching

Posted 2021-05-09

def binarySearch(alist, item):
  '''
  Function: binarySearch
  Description: Binary search on list
  Input: List
  Output: Tuple of boolean, index
  Usage: binarySearch(list, item)
  Notes: Does not edit list in place, recursive
  '''
	    if len(alist) == 0:
	        return False
	    else:
	        midpoint = len(alist)//2
	        if alist[midpoint]==item:
	          return (True, midpoint)
	        else:
	          if item<alist[midpoint]:
	            return binarySearch(alist[:midpoint],item)
	          else:
	            return binarySearch(alist[midpoint+1:],item)
	
testlist = [0, 1, 2, 8, 13, 17, 19, 32, 42,]
print(binarySearch(testlist, 3))
print(binarySearch(testlist, 13))


def binarySearch(alist, item):
  '''
  Function: binarySearch
  Description: Binary search on list
  Input: List
  Output: Tuple of boolean, index
  Usage: binarySearch(list, item)
  Notes: Does not edit list in place, recursive
  '''
    first = 0
    last = len(alist)-1
    found = False

    while first<=last and not found:
        midpoint = (first + last)//2
        if alist[midpoint] == item:
            found = True
	        else:
	            if item < alist[midpoint]:
	                last = midpoint-1
	            else:
	                first = midpoint+1
	
	    return found
	    
	    
	    
testlist = [0, 1, 2, 8, 13, 17, 19, 32, 42,]
19	print(binarySearch(testlist, 3))
20	print(binarySearch(testlist, 13))

def sequentialSearch(alist, item):
  '''
  Function: sequentialSearch
  Description: Sequential search on list
  Input: List
  Output: Tuple of boolean, index
  Usage: SequentialSearch(list, item)
  Notes: Does not edit list in place
  '''
    pos = 0
    found = False
	
    while pos < len(alist) and not found:
        if alist[pos] == item:
            found = True
        else:
            pos = pos+1
	
    return (found, pos)
	
testlist = [1, 2, 32, 8, 17, 19, 42, 13, 0]

print(sequentialSearch(testlist, 3))
print(sequentialSearch(testlist, 13))

haystack=["Zig","Zag","Wally","Ronald","Bush","Krusty","Charlie","Bush","Bozo"]
b = [ "Zig", "Bush" ] 
 
def find_index(lista, listb):

    for needle in listb:
        try:
            print (lista.index(needle), needle)
        except ValueError, value_error:
            print (needle,"is not in haystack")
            
            
print (find_index(haystack, b))

haystack=["Zig","Zag","Wally","Ronald","Bush","Bush","Krusty","Charlie","Bush","Bozo"]
b = [ "Zig", "Bush" ] 
 
def find_index(lista, listb):
    dicta = dict()
    
    for needle in listb:
        try:
            #print (lista.index(needle), needle)
            if needle not in dicta:
                dicta[needle] = []
                dicta[needle].append(lista.index(needle))
            else:
                dicta[needle].append(lista.index(needle))
        except ValueError:
            print (needle,"is not in haystack")
    return dicta            
            
print (find_index(haystack, b))

Functions that search for a specific element in a list, and return its index.
  1. binarySearch         = Binary search on array (fastest)
  2. SequentialSearch     = Sequential search on array (slowest)
  3. index_search         = Sequential search, returns indices of match
  4. dict_index_search    = Sequential search, stores matches in dictionary