binary_search_code

# 4.8 (102) python bisection search code by Raspary pi (Furure Learn) modified by Ken Adams
#Uses the function 'binary_search' binary method to search a list for a given value.
#If the value is not there it can return False or return the nearest item on the list
# Unfortunately with the code at present (x integer)  x.5 would get round down to x instead of up to x+1
# Another function 'run_binary_search_smallest' will return the lowest index available for an item on the list.

#my_list=[1, 2, 3, 4, 4, 4, 4, 4, 5, 6, 7, 8, 9]
my_list = [1,2,3,5,6,7]
my_value = 3

def binary_search(sorted_list, value,near):# near is set to 1 if you cant get exact but will accept the nearest
    # left to 0
    left = 0
    # right to highest index in list
    right = len(sorted_list) - 1
    # loop that ends when left > right
    while left <= right:
        # mid to int between left and right
        mid = int((right + left)/2)
        # if sorted_list[mid] > value  set right to mid
        if sorted_list[mid] > value:
            right = mid - 1
        # if sorted_list[mid] < value  set left to mid
        elif sorted_list[mid] < value:
            left = mid + 1
        # if sorted_list[mid] == value  return mid
        else:
            return mid
    # loop ends return `False`

    ###############################looking for the nearst
    if near == 1:
        print("finding the closest")
        if mid == 0: # have searched to the botom of the list so value must be below the bottom
            return 0
        elif mid == len(sorted_list)-1: # have searched to top of list go value beyoud that
            return mid
        else:
            closest = mid-1 #any of the three mid-1, mid, mid+1 could fetch the closest
            # we start at closest = mid-1 and use a for loop to change that if nessary
            for i in range(2):
                if abs(sorted_list[closest]-value) > abs(sorted_list[closest+1]-value):
                    closest = closest +1
            return closest
    return False # f near was not set to one the if above is not used so we return False as usual

# function to find lowest
def run_binary_search_smallest(my_list, my_number): #uses their binary_search not my own
    first = binary_search(my_list, my_value,)# get one place to start
    while my_list[first] == my_number and first >= 0:
        store_first = first #store the result of the last loop throught the while
        first  -= 1 # decrement first
    return store_first
# CHOOSE WHAT FUNCTION TO RUN
position = binary_search(my_list, my_value,1)
#position = run_binary_search_smallest(my_list, my_value)
print(position)
print("Looking for " + str(my_value) + " The item at position " + str(position) + " is " +str(my_list[position]))

print("bye")