How do I run a binary search for words that start with a certain letter?

Question

I am asked to binary search a list of names and if these names start with a particular letter, for example A, then I am to print that name. I can complete this task by doing much more simple code such as

for i in list:
    if i[0] == "A":
        print(i)

but instead I am asked to use a binary search and I'm struggling to understand the process behind it. We are given base code which can output the position a given string. My problem is not knowing what to edit so that I can achieve the desired outcome

name_list = ["Adolphus of Helborne", "Aldric Foxe", "Amanita Maleficant", "Aphra the Vicious", "Arachne the Gruesome", "Astarte Hellebore", "Brutus the Gruesome", "Cain of Avernus"]


def bin_search(list, item):
    low_b = 0
    up_b = len(list) - 1
    found = False

    while low_b <= up_b and found ==  False:
        midPos = ((low_b + up_b) // 2)
        if list[midPos] < item:
            low_b = midPos + 1
        elif list[midPos] > item:
            up_b = midPos - 1
        else:
            found = True
    if found:
        print("The name is at positon " + str(midPos))
        return midPos
    else:
        print("The name was not in the list.")

Desired outcome

bin_search(name_list,"A")

Prints all the names starting with A (Adolphus of HelBorne, Aldric Foxe .... etc)

EDIT: I was just doing some guess and check and found out how to do it. This is the solution code

def bin_search(list, item):
    low_b = 0
    up_b = len(list) - 1
    true_list = []
    count = 100
    while low_b <= up_b and count > 0:
        midPos = ((low_b + up_b) // 2)
        if list[midPos][0] == item:
            true_list.append(list[midPos])
            list.remove(list[midPos])
            count -= 1
        elif list[midPos] < item:
            low_b = midPos + 1
            count -= 1
        else:
            up_b = midPos - 1
            count -= 1
    print(true_list)

Answer 1

Not too sure if this is what you want as it seems inefficient... as you mention it seems a lot more intuitive to just iterate over the entire list but using binary search i found here i have:

def binary_search(seq, t):
    min = 0
    max = len(seq) - 1
    while True:
        if max < min:
            return -1
        m = (min + max) // 2
        if seq[m][0] < t:
            min = m + 1
        elif seq[m][0] > t:
            max = m - 1
        else:
            return m

index=0
while True:
    index=binary_search(name_list,"A")
    if index!=-1:
        print(name_list[index])
    else:
        break
    del name_list[index]

Output i get:

Aphra the Vicious
Arachne the Gruesome
Amanita Maleficant
Astarte Hellebore
Aldric Foxe
Adolphus of Helborne

Answer 2

You just need to found one item starting with the letter, then you need to identify the range. This approach should be fast and memory efficient.

def binary_search(list,item):
    low_b = 0
    up_b = len(list) - 1
    found = False
    midPos = ((low_b + up_b) // 2)
    if list[low_b][0]==item:
        midPos=low_b
        found=True
    elif list[up_b][0]==item:
        midPos = up_b
        found=True
    while True:
        if found:
            break;
        if list[low_b][0]>item:
            break
        if list[up_b][0]<item:
            break
        if up_b<low_b:
            break;
        midPos = ((low_b + up_b) // 2)
        if list[midPos][0] < item:
            low_b = midPos + 1
        elif list[midPos] > item:
            up_b = midPos - 1
        else:
            found = True
            break
    if found:
        while True:
            if midPos>0:
                if list[midPos][0]==item:
                    midPos=midPos-1
                    continue
            break;
        while True:
            if midPos<len(list):
                if list[midPos][0]==item:
                    print list[midPos]
                    midPos=midPos+1
                    continue
            break
    else:
        print("The name was not in the list.")

the output is

>>> binary_search(name_list,"A")
Adolphus of Helborne
Aldric Foxe
Amanita Maleficant
Aphra the Vicious
Arachne the Gruesome
Astarte Hellebore